AU696986C - Novel proteins which bind to retinoblastoma protein and their encoding DNA equences - Google Patents

Description

DESCRIPTION

NOVEL PROTEINS WHICH BIND

TO RETINQBLASTOMft PROTEIN

AND THEIR ENCODING DNA SEQUENCES

BACKGROUND OF THE INVENTION

The government owns rights in the present invention pursuant to grant number CA49649 from the National Institutes of Health.

Field of the Invention

The present invention relates generally to the field of cellular regulation. More particularly, it concerns the control of cell growth as affected by the retinoblastoma protein, the implications of this control in cancers including retinoblastoma, and the interactions of oncogenes with cell cycle control proteins and other retinoblastoma associated cellular proteins.

Description of the Related Art

Retinoblastoma is a malignant cancer of the developing retina that manifests itself as an intraocular tumor in early childhood (Shields, J.A. , 1993). Retinoblastoma occurs in two distinct forms (Vogel, F., 1979) . In close to 40% of retinoblastoma cases, tumors appear bilaterally, may be multifocal in each eye, and appear at a very young age. Bilateral retinoblastoma is sometimes diagnosed in newborn infants. In the remaining retinoblastoma cases, tumors are unilateral, are unifocal, and generally present at about 2 years of age. The pattern of inheritance of retinoblastoma suggests that the wild-type alleles encode a repressor of tumor formation (Migdal, C, 1976) . Evidence for the existence of tumor-suppressing genetic factors is also provided by cell fusion studies. Upon fusion of tumor cells with normal fibroblasts, lymphocytes, or keratinocytes (Harris, H., 1986a; Klein, G., et al . , 1971) , the malignant properties of the original tumor cells are suppressed.

A candidate for the retinoblastoma suppressor gene (Rb) has been cloned, and extensive structural and functional analysis of the gene and its gene product has begun (Goodrich and Lee, 1993) . The Rb gene product has properties that suggest a role in regulation of the cell division cycle. For example, Rb protein forms complexes with many cellular and viral proteins, including transcription factors, that influence the cell cycle. The purified Rb protein can also arrest Gl phase progression of the cell cycle when introduced by microinjection. Also, the protein is phosphorylated in a cell cycle dependent manner, suggesting that Rb may be cyclically regulated.

Deletions within the Rb gene have been defined in an extensive number of retinoblastomas (Lee, .-H., et al., 1987a, 1987b) . In addition, about 12-30% of retinoblastomas have detectable genomic rearrangement of Rb, and it is believed that other undetectable small and deletions are present but go unnoticed. In one particular study, a large number of retinoblastoma cell lines and primary tumors were screened and none were detected with normal expression of the Rb protein (Horowitz, J.M., et al . , 1990) . It is believed that no retinoblastoma primary tumor or cultured cell has been reported to have normal expression of the wild-type Rb gene product. In addition, mutations in the Rb gene have been implicated in other types of cancer such as osteosarcomas, and soft tissue sarcomas (Weichselbaum, R.R. , et al . , 1988) .

An interesting biochemical property of the Rb gene product is its ability to form specific complexes with the transforming proteins of several DNA tumor viruses including SV40 large T, adenovirus E1A, and human papillomavirus E7 (DeCaprio, J.A. , et al . , 1988; Dyson, N., et al., 1989a; Whyte, P., et al., 1988) . The regions of the transforming proteins required for complex formation with Rb are similar to those required for transformation of cells. The amino acids of Rb protein required for binding to SV40 T antigen have also been determined (Huang, S., et al . , 1990), and the regions of these amino acids correspond to those frequently mutated in tumor cells. For example, in all cases analyzed to date, mutated Rb proteins from human tumor cells have been unable to form complexes with T antigen. This correlation between the T antigen binding domains and the naturally occurring mutations in cancer cells suggests that these regions constitute an important functional domain.

It is suggested that DNA tumor viruses induce transformation by binding a more active, unphosphorylated form of the Rb protein, thereby inhibiting its normal, suppression function (Ewen, M.E., et al . , 1989) . The mechanism of transformation by DNA tumor viruses, however, may be more complex than simple inactivation of Rb. Several reports have indicated that binding Rb protein is not sufficient to induce the full transformation potential of some DNA tumor viruses (Manfredi and Prives, 1990; Weber, J.M., et al . , 1991) . However, binding of DNA tumor virus transforming proteins has pinpointed a region of Rb that is required for protein association and may be important for its normal function.

What is needed, then is a method of regulating cell growth and blocking tumorigenesis through the control of tumor suppressor proteins in their interaction with oncogene products. This control is possible through the interaction of these tumor suppressors and the cellular proteins that bind at functional sites and modulate their biological activity.

Ras mutations occur in 90% of pancreatic tumors. Many other tumors have been found to have mutations in Ras, or in tumor suppressor proteins such as E2F, p53 or Rb. The ability of p48 to bind Rb in a crucial area for the tumor suppressor activity combined with its ability to suppress a Ras mutation phenotype indicate that this protein is an important factor in the tumorigenesis event. It is contemplated that suppression of tumor growth will be possible by decreasing the concentration of p48 in cells by, for example the introduction of antisense RNA complementary to the DNA sequences disclosed in the present invention. Alternatively, p48 levels may be increased by the transfection of tumor cells with the vectors of the present invention.

In an alternative embodiment, the polypeptide and nucleic acid sequences of the present invention will be useful to screen for mutations in the p46 or p48 genes which may be related to the inherited tendency to develop certain types of cancer. The knowledge of whether a patient carries a heterozygous mutation in these important genes will have important implications for gene therapy and genetic counseling.

The ability to screen cell lines for functional mutations in the Rb gene is also an embodiment of the present invention. Since it is known that the viral transforming proteins bind in the same region of Rb as does p48 and p46, these proteins provide a way to screen the lysates of cells to determine whether the Rb protein produced by these cells contains mutations in this important region. Again, this ability to quickly screen for these mutations has valuable implications for gene therapy and for genetic counseling.

In certain embodiments, the invention concerns DNA segments or even genes encoding novel Rb binding proteins. In this respect, the term "gene" is used for simplicity to refer to a functional protein or peptide encoding unit. As will be understood by those in the art, this functional term includes both genomic sequences and cDNA sequences. More particularly, the invention concerns DNA segments encoding the protein termed p48, DNA segments encoding the protein termed p46 and, also, DNA segments encoding peptide or polypeptide fragments of such proteins. As used herein, the term "DNA segment" is intended to refer to a DNA molecule which has been isolated free of total genomic DNA of a particular species, or in particular isolated away from, or purified free from, total genomic DNA of the species from which the DNA is obtained, such as, e.g., mammalian DNA.

Included within the term "DNA segment", are DNA segments which may be employed in the preparation of vectors, as well as the vectors themselves, including, for example, plasmids, cosmids, phage, viruses, and the like.

In certain aspects, the invention is directed to DNA segments and recombinant vectors comprising an isolated gene encoding a p48 or p46 protein of polypeptide, and preferably, a p48 or p46 protein which is capable of interacting with retinoblastoma protein (Rb) . The p48 protein or polypeptide will include an amino acid sequence in accordance with the amino acid sequence set forth in SEQ ID NO:2, or a portion or biological functional equivalent thereof, whereas the p46 protein or polypeptide will include an amino acid sequence in accordance with the amino acid sequence set forth in SEQ ID NO:10, or a portion of biological function equivalent thereof.

In other particular embodiments, the invention concerns isolated DNA segments and recombinant vectors which include a nucleic acid sequence in accordance with a continuous segment or segments of the nucleic acid sequences set forth in SEQ ID NO:l and SEQ ID NO:9. Preferred vectors will generally be those which include, or have, the specific nucleic acid sequence of SEQ ID NO:l and those which include, or have, the specific nucleic acid sequence of SEQ ID NO:9.

The term "capable of interacting with the retinoblastoma protein" means that upon contacting the retinoblastoma protein, with the p48 or p46 protein, for example, under appropriate conditions of ionic strength, temperature, pH and the like, specific binding will occur. The interaction may occur due to specific electrostatic, hydrophobic, entropic or other interaction of certain amino acid or glycolytic residues of the one protein, Rb, with specific amino acid or glycolytic residues of the second protein, particularly p46 or p48, to form a stable complex under the conditions effective to promote the interaction. The interaction may alter the three dimensional conformation of either or both proteins or polypeptides involved in the interaction and it may also alter the function or activity of either or both proteins or polypeptides involved in the interaction. For example, the interaction of Rb with p48 or p46 may alter the ability of Rb to bind other proteins, such as SV40 T antigen, to bind small molecules, to bind or recognize specific regions of DNA, to act as a substrate for a phosphorylation or dephosphorylation or other enzymatic reaction, or to catalyze or effect any enzymatic reaction involving other substrates and reactants.

In light of the preceding discussion, it will also be understood that the entire length of the Rb, p48 and/or p46 proteins may not be necessary for a specific binding interaction to occur. A smaller polypeptide comprising a portion of the sequence of p48 of p46, such as, for example, a polypeptide of between 300 and about 400 amino acids, or a polypeptide of between 100 and about 200 amino acids, or even polypeptides of between 50 and about 75 amino acids which comprise a portion of the sequence according to SEQ ID NO:2 or SEQ ID NO:10 would be able to interact with Rb and would be encompassed by the present invention. It is also contemplated that smaller polypeptides comprising portions of the amino acid sequence of p46 or p48 of between 20 and about 40 amino acids would be useful in the present invention and that even polypeptides of about 4, 10, or even 15 amino acids which comprise a portion of the sequence according to SEQ ID NO:2 or SEQ ID NO:10 would bind to Rb or would be useful as epitopic core sequences for the production of antibodies to p48 or p46. It is also understood that only a portion of the Rb protein, the carboxy terminal region, for example, may be involved in the interaction.

p48 or p46 protein constructs may also be prepared in which all or a portion of the sequence of SEQ ID NO:2 or SEQ ID NO:10 is covalently joined to other amino acid segments, including, but not limited to amino acid segments derived from the sequence of Rb, and amino acid segments which have marker functions or are otherwise detectable. All such fusion polypeptides fall within the scope of the present invention. Particularly useful recombinant vectors are contemplated to be those vectors, such as plasmids, in which the coding portion of the DNA segment is positioned under the control of a promoter. Such vectors are referred to as "recombinant expression vectors" and they may be generally defined as vectors which are capable of expressing a p48 or p46 protein or polypeptide following their introduction into a host cell, thereby creating a recombinant host cell . Vectors capable of being transformed into, and expressed in, recombinant yeast cells are preferred in certain embodiments. Recombinant plasmids and multicopy plasmids are also preferred, with vectors derived from the plasmid YEpl3 , for example plasmid YEp24 (New England Biolabs) being particularly preferred.

In expression vectors, the promoter may be in the form of the promoter which is naturally associated with a p48 or p46 gene in mammalian cells. Such a promoter may be obtained by isolating the 5' non-coding sequences located upstream of the coding segment or exon, for example, using recombinant cloning and/or PCR technology in connection with the compositions disclosed herein, particularly the more 5' regions of the p48 and p46 sequences.

In other embodiments, it is contemplated that certain advantages will be gained by positioning the coding DNA segment under the control of a recombinant, or heterologous, promoter. As used herein, a recombinant or heterologous promoter is intended to refer to a promoter that is not normally associated with a p48 or p46 gene in its natural environment. Such promoters may include promoters normally associated with other mammalian genes, and/or promoters isolated from any other bacterial, viral or eukaryotic gene. Naturally, it will be important to employ a promoter that effectively directs the expression of the DNA segment in the cell type chosen for expression.

Recombinant host cells, including prokaryotic and eukaryotic cells, form another aspect of this invention. In general terms, a recombinant host cell prepared in accordance with the present invention will include a DNA segment or recombinant vector encoding a p48 or p46 protein or polypeptide which includes an amino acid sequence in accordance with SEQ ID NO:2 or SEQ ID NO:10, respectively, or a portion or biological functional equivalent thereof. In preferred embodiments, the DNA segment will be introduced into a cell in the form of a recombinant expression vector, and the resultant recombinant host cell will be capable of expressing recombinant p48 or p46 proteins or polypeptides.

Expression vectors may be employed to express p48 or p46 proteins, polypeptides or peptides in a variety of recombinant host cells, including, by way of example, yeast cells. The use of promoter and cell type combinations for protein expression is generally known to those of skill in the art of molecular biology, for example, see Sambrook et al . (1989) . The promoters employed may be constitutive, or inducible, and can be used under the appropriate conditions to direct high level expression of the introduced DNA segment, such as is advantageous in the large-scale production of recombinant p48 or p46 proteins or peptides. The preferred promoter system contemplated for use in high- level expression includes, but is not limited to ADHI (Berer and Young, 1982) .

In connection with expression embodiments to prepare recombinant p48 or p46 proteins and peptides, it is contemplated that longer DNA segments will most often be used, with DNA segments encoding functional domains or the entire p48 or p46 proteins being most preferred. However, it will be appreciated that the use of shorter DNA segments to direct the expression of p48 or p46 peptides or epitopic core regions, such as may be used to generate anti-p48 or anti-p46 antibodies, also falls within the scope of the invention.

In addition to their use in directing the expression of p48 or p46 proteins, the nucleic acid sequences disclosed herein also have a variety of other uses. For example, they also have utility as probes or primers in nucleic acid hybridization embodiments. As such, it is contemplated that oligonucleotide fragments corresponding to the sequence of SEQ ID N0:1 or SEQ ID NO:9 for stretches of between about 10 to 15 nucleotides and about 20 to 30 nucleotides will find particular utility. Longer complementary sequences, e.g., those of about 40, 50, 100, 200, 500, 1000, and even up to full length sequences of about 2291 nucleotides in length for SEQ ID NO:l, and 1668 nucleotides in length for SEQ ID NO:9, will also be of use in certain embodiments.

The ability of such nucleic acid probes to specifically hybridize to p48-encoding or p46-encoding sequences will enable them to be of use in detecting the presence of complementary sequences in a given sample. However, other uses are envisioned, including the use of the sequence information for the preparation of mutant species primers, or primers for use in preparing other genetic constructions.

Nucleic acid molecules having stretches of 10, 20, 30, 50, or even of 100 nucleotides or so, complementary to SEQ ID NO:l or SEQ ID NO:9 are particularly contemplated as hybridization probes for use in, e.g.,

Southern and Northern blotting. This would allow p48 or p46 structural or regulatory genes to be analyzed, both in diverse cell types and also in various patients or in other mammalian cells. The total size of fragment, as well as the size of the complementary stretch(es) , will ultimately depend on the intended use or application of the particular nucleic acid segment. Smaller fragments will generally find use in hybridization embodiments, wherein the length of the complementary region may be varied, such as between about 10 and about 100 nucleotides, but larger complementary stretches of up to about 2291 (SEQ ID NO:l) or 1668 (SEQ ID NO: 9) nucleotides may be used, according to the length complementary sequences one wishes to detect.

The nucleic acid segments of the present invention, regardless of the length of the coding sequence itself, may be combined with other DNA sequences, such as promoters, polyadenylation signals, additional restriction enzyme sites, multiple cloning sites, other coding segments, and the like, such that their overall length may vary considerably. It is therefore contemplated that a nucleic acid fragment of almost any length may be employed, with the total length preferably being limited by the ease of preparation and use in the intended recombinant DNA protocol. For example, nucleic acid fragments may be prepared which include a short stretch complementary to SEQ ID NO:l or SEQ ID NO:9, such as about 10 nucleotides, and which are up to 10,000 or 5,000 base pairs in length, with segments of 3,000 being preferred in certain cases. DNA segments with total lengths of about 1,000, 500, 200, 100 and about 50 base pairs in length are also contemplated to be useful .

It will also be understood that this invention is not limited to the particular nucleic acid and amino acid sequences of SEQ ID NOs:l, 2, 9 and 10, and the other disclosed herein. Recombinant vectors and isolated DNA segments may therefore variously include p48 or p46 coding regions themselves, coding regions bearing selected alterations or modifications in the basic coding region, or they may encode larger polypeptides which nevertheless include p48-coding or p46-coding regions or may encode biologically functional equivalent proteins or peptides which have variant amino acids sequences.

The DNA segments and proteins of the present invention encompass biologically functional equivalent p48 and p46 proteins and peptides. Such sequences may arise as a consequence of codon redundancy and functional equivalency which are known to occur naturally within nucleic acid sequences and the proteins thus encoded. Alternatively, functionally equivalent proteins or peptides may be created via the application of recombinant DNA technology, in which changes in the protein structure may be engineered, based on considerations of the properties of the amino acids being exchanged. Changes designed by man may be introduced through the application of site-directed mutagenesis techniques. If desired, one may also prepare fusion proteins and peptides, e.g., where the p48 or p46 coding regions are aligned within the same expression unit with other proteins or peptides having desired functions, such as for purification or immunodetection purposes.

In further embodiments, the invention concerns methods for using DNA segments which encode p48 or p46 proteins or polypeptides. One such method of use involves utilizing such novel DNA sequences and segments in processes to prepare compositions which include p48 or p46 proteins or polypeptides, and preferably, substantially purified p48 or p46 proteins or polypeptides. In a general sense, these methods of using DNA include preparing a recombinant vector in which the DNA coding segment is positioned under the control of a promoter and introducing the recombinant vector into a host cell . One would then culture the host cell under conditions effective to allow expression of the encoded p48 or p46 protein or polypeptide, and collect the protein or polypeptide thus expressed.

In preferred embodiments, it is contemplated that one would prepare a recombinant plasmid vector capable of expressing a recombinant p48 or p46 protein, polypeptide or peptide, and introduce the plasmid into a recombinant host cell, most preferably, a yeast cell. One would then produce recombinant p48 or p46 by culturing the recombinant yeast cells under conditions effective to obtain the p48 or p46 protein or polypeptide.

The present invention also encompasses compositions, free from total cellular components, which comprise p48 or p46 protein or polypeptides, and preferably, substantially purified p48 or p46 proteins and polypeptides. Such proteins may either be recombinant p48 or p46, preferably obtained from p48-expressing or p46-expressing recombinant yeast cells. Alternatively, the p48 or p46 may be so-called native or natural p48 or p46, as isolated and purified from non-recombinant cells, such as human HeLa cells, which express p48 and p46 in the nucleus.

In general, p48 or p46 compositions may be prepared by obtaining an extract from p48-containing or p46- containing cells, whether native or recombinant, subjecting the extract to fractionation and collecting a fraction containing the p 8 or p46 protein or polypeptide. In more detail, this includes identifying a positive fraction containing a p48 or p46 protein or polypeptide capable of interacting with the retinoblastoma protein (Rb) , and collecting the positive fraction or fractions separately from the other fractions. In this manner, p48 or p46 proteins can be provided essentially free from non-p48 and non-p46 components. A preferred process for extract fractionation is affinity chromatography using a retinoblastoma protein (Rb) affinity column.

In addition to full-length p48 and p46 proteins, such as proteins which have a sequence in accordance with SEQ ID NO:2 or SEQ ID NO:10, smaller polypeptides and peptides are also included within the proteinaceous p48 and p46 compositions of present invention. For example, peptides of between about 15 to about 50 amino acids in length, or preferably, of about 15 to about 30 amino acids in length are contemplated.

In still further aspects, the invention concerns anti-p48 and anti-p46 antibody compositions. These include polyclonal and monoclonal antibodies which recognize both the p46 and p48 proteins, although the generation of antibodies which are specific for either the p48 protein or the p46 protein is also contemplated. An antibody prepared in accordance with the present invention may generally be defined as one having binding affinity for p48 or p46 protein or polypeptide which is capable of interacting with Rb and which include a sequence in accordance with the amino acid sequences set forth in SEQ ID NO:2 or SEQ ID NO:10, or a portion or functional equivalent thereof. The antibodies may be either polyclonal or monoclonal, the latter being exemplified in certain preferred embodiments by the monoclonal antibody termed 13D10 which is disclosed herein.

The p48 and p46 DNA, protein and antibody compositions of the present invention will be useful in a variety of different embodiments. For example, it may now be determined for the first time whether mutations in p48 or p46 correlate with the presence of tumors in human subjects and patients. This may be done either at the DNA level, using the DNA segments of the invention in any of the nucleic acid hybridization embodiments described herein and known to those of skill in the art, including SSCP (single strand conformation polymorphism) and ribonuclease protection assays which can be used to detect mutations in p48 and/or p46 genes. Equally, diagnostic assays may be conducted at the protein level, e.g., using Western blotting or immunohistochemical analyses. Such techniques may be used to determine whether the protein conformations are changed or whether mutant forms of the proteins exist and correlate with transformed phenotype (s) . In addition, it will be significant to discover whether mutations in the p48 or p46 gene may mask or complement mutations in the Rb gene, thereby restoring the tumor suppressing function.

In any event, positive correlations between mutations in p46 or p48, or even in expression levels of either protein and tumorigenesis allow the use of either the nucleic acid segments or polypeptide segments and antibodies thereof of the invention to detect tumor cells, i.e., use as diagnostic or prognostic tools in the detection and monitoring of cancer. The use of the nucleic acid segments, proteins and antibodies thereto of the present invention are also useful to determine if a negative correlation exists. Indeed, if a positive correlation does not exist, it will be of significant value to determine this fact.

The effect of p48 or p46 binding to Rb protein will also have utility in aspects of Rb function other than in its anti-oncogenic capacity. For example, the Rb protein is believed to play a general role in the regulation of cell growth (Lee et al . , 1991) . This is based on the facts that the phosphorylation state of Rb is cyclic and corresponds to the cell growth cycle, Rb has co- precipitated with the CDC2 complex, and the Rb sequence contains several CDC2 consensus phosphorylation sites. CDC2 is considered to be the principal controller of cell cycle progression in all eukaryotic cells (Draetta, 1990) , and thus, proteins that interact with this complex will have utility in a wide range of biological and medical applications involved in development and growth or organisms and tissues, such as treatment of damaged or atrophied organs, the growth of particular organ tissue for implantation and for wound healing.

A further example of the usefulness of the proteins and peptides of the present invention is embodied in the inventors' discovery that p48 can suppress the heat shock phenotype in a yeast strain carrying a Ras mutation. It is contemplated that p48, and the highly conserved, related protein, p46, can suppress the activity of oncogenic Ras in mammalian cells, and thus that p48 or p46 may be used to suppress the oncogenic p21 Ras in a variety of human tumor types ranging from leukemias to colorectal carcinomas. Pharmaceutical preparations of p48 and p46 compositions formulated in pharmacologically- acceptable vehicles therefore form yet another aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 depicts the molecular cloning of RbAp48. Figure 1 contains parts A-B.

Figure IA illustrates the specific interaction between Rb and cellular proteins that bound to the Rb- affinity column. Binding sites in Rb were blocked with either T peptide (left panel) or K peptide (right panel) prior to the addition of the HeLa cell lysate; bound proteins were dissolved in 2-D sample buffer and analyzed on an isoelectric focusing gel.

Figure IB is the cDNA sequence (SEQ ID NO:l) and the deduced amino acid sequence (SEQ ID NO:2) of RbAp48. The 2,230 nucleotides of the p48 cDNA are shown with the predicted amino acid products (single-letter amino acid code) . The numbers correspond to the nucleotide (upper line in each pair) or amino acid (lower line in each pair) . An open reading frame of 425 amino acid residues is shown. Arrows indicate the location of the primers used in the PCR reaction. Peptide sequences identical to those obtained from the purified protein are underlined.

Figure 2 is a demonstration that RbAp48 is a full- length cDNA encoding p48. Figure 2 contains parts A-C.

Figure 2A depicts the products of the in vi tro translation of RbAp48 mRNA transcripts. Lane 1 contained no RNA. Transcripts from constructs pGEM-.R-Ap48 (lane 2) and ^■ph-RbAp48 (containing 5' non-coding sequences of β- globin mRNA, lane 3) were used for in vi tro translation. The ^JJS-labeled translation products were either directly analyzed by 10% SDS-polyacrylamide gel (lanes 1-3) or analyzed after immunoprecipitation with anti-p48 monoclonal antibody 13D10 (lane 4) . The translation efficiency of the chimeric construct containing the 5' untranslated region of the 3-globin gene and the coding region of the RbAp48 was found to be 20-fold greater than that of the original RbAp48 clone. This is consistent with a previous report of enhanced translation after the replacement of the 5' untranslated region (Jobling and Gehrke, 1987) .

Figure 2B demonstrates that p48 from the in vi tro translation reaction and p48 from the eluate of the Rb- affinity column have similar mobility in an SDS-PAGE analysis. p48 in the eluate (lane 1) or from the in vi tro translation reaction (lane 2) were separated by a 10% SDS-PAGE and detected by western blotting with monoclonal antibody 13D10.

Figure 2C shows the immunoreactivity of antibody 13D10 with p48 on a 2-D gel. Rb matrices were incubated with a mixture of radiolabeled and unlabeled HeLa cell lysates. Bound proteins were separated by 2-D gel electrophoresis and visualized by immunoblotting with 13D10 (right panel) , followed by fluorography (left panel) . The arrow indicates the p48 spot detected by antibody 13D10.

Figure 3 demonstrates the interaction of Rb and p48 in vivo and in vi tro. Figure 3 contains parts A-C.

Figure 3A is a gel in which lysates were prepared from 6 cell lines; HeLa (lane 1) , Weri-27 (lane 2) , Du- 145 (lane 3) , SaoS-2 (lane 4), SCLC-SD-1 (lane 5) , Molt-4 (lanes 6-9) . Equal amounts of total protein (38 mg) were aliquoted for immunoprecipitation using anti-Rb 0.495 (lanes 1-6 & 9) , anti-p48 13D10 (lane 8) or normal serum (lane 7) . The immunoprecipitates were separated by denaturing gel electrophoresis, transferred to a membrane and incubated with anti-p48 antibody 13D10 (lane 1-6) or anti-Rb 3C8 (lane 7-9) .

Figure 3B shows the result of an immunoprecipi- tation. Molt-4 cells were labeled with -"s-methionine and lysed as described above. The lysate was first immunoprecipitated with either anti-Rb antibody 0.495 or anti-p48 antibody 13D10. The resulting immune complexes were boiled in the presence of 2% SDS to dissociate protein complexes, and the denatured proteins were diluted for reimmunoprecipitation with the indicated antibodies. Normal culture supernatant for hybridoma (NCS) , normal rabbit serum (NRS) , rabbit anti-nm23 antibody 2669 (unpublished) , and PAB419 (Harlow et al . , 1981) were used as negative controls. In the samples where 13D10 or 0.495 immunoprecipitates were reimmuno- precipitated with the same antibodies, only one-tenth of the samples were loaded onto the gel .

Figure 3C demonstrates direct binding between p56^ΛU and p48. In the left panel, purified p56 , p48, and a mixture of p56^" and p48 were separated by native polyacrylamide gel electrophoresis and visualized by silver staining. In the right panel, a new band seen in the p56^R" and p48 mixture was excised and the proteins were separated on a 10% SDS-polyacrylamide gel and visualized by silver staining.

Figure 4 shows the effect of p48 expression on the heat shock sensitivity of yeast strains containing _RAS2Vαll9 _and y_east strains lacking iral . The top left and right plates indicate the heat shock resistance of yeast strains TK161-R2V, carrying RAS2^Vαl19 , after transformation with the various indicated plasmids: A control with no plasmid; pd3, a plasmid expressing yeast MSI1 under its own promoter; pd3::48K, a plasmid expressing human p48 from the yeast MSI1 promoter; and YEp24, the vector from which pd3 is derived are shown. One of the replicate plates containing the transformant patches was incubated at 30°C (left) , and the other was incubated at 57°C prior to incubation at 30°C (right) . The bottom left and right plates show the heat shock resistance of yeast strains KT6-1A-D, which contain a disrupted chromosomal iral gene after transformation and incubation as in the upper plates.

Figure 5 is the nucleic acid sequence of the cDNA, RbAp46, and is designated SEQ ID NO:9. Figure 6 is the deduced amino acid sequence of the protein, p46, and is designated SEQ ID NO:10.

Figure 7 is the amino acid sequences of p46, SEQ ID NO:2 and p48, SEQ ID NO:10, aligned to illustrate the homology of the two sequences.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The growth suppression function of the retinoblastoma protein (Rb) is thought to be mediated by Rb binding to cellular proteins (Goodrich et al . , 1993) . The range of proteins that associate with Rb in vi tro is quite large and includes transcription factors, oncogenes, structural proteins, possible signal transducing proteins, kinases, and phosphatases (Shan et al . , 1992) . One of these Rb binding proteins, p48 forms complexes with Rb in vi tro and in vivo . This complex formation apparently involves direct interaction between these two ubiquitously expressed nuclear proteins.

An important embodiment of the present invention is the isolation and sequencing of two full-length complementary DNAs, RbAp48 encoding p48 and RbAp46 encoding p46. The two proteins, p48 and p46 share 95% amino acid sequence homology and exhibit crossreactivity with several monoclonal and polyclonal antibodies. It is contemplated, therefore, that the two proteins have similar functions. The 5' and 3' untranslated regions of the RbAp46 clone are significantly different than those regions of the RbAp48 clone, suggesting that these very similar proteins are the products of separate genes. The clones appear to be full-length based on the sequence data and because the putative methionine initiation codon of RbAp48 is surrounded by sequences that resemble the consensus sequence for preferred translational start sites (Kozak, 1984) . Also, the DNA sequences upstream from this codon are G+C-rich, and analysis of the codon usage in this region suggests they are non-coding sequences. Further evidence is provided by in vi tro translation reactions using transcripts generated from the RbAp48 cDNA, which yield a major protein of 48 kDa (Fig. 2A, lane 2-4, Fig. 2B, lane 2) that co-migrated with the p48 in the eluates of the Rb-affinity columns (Fig. 2B, lane 1) .

Another important embodiment of the present invention is the presence of repetitive sequences in the deduced amino acid sequences of p48 and p46. Similar internal repeats have been found in proteins involved in a wide spectrum of cellular functions, including Ste4 in yeast pheromone signal transduction, Cdc4 and Cdc20 in yeast cell cycle control, Tupl in yeast cell identity, sporulation and metabolic repression, etc. (Goebl and Yanagida, 1991) . Although the functional significance of the conserved amino acid residues is unknown, site- specific mutagenesis of the tryptophan and aspartic acid residues that occur in these internal repeats, performed in the inventors' laboratory, reveals that these amino acids are important for p48 function in yeast.

Another important aspect of the present invention involves the central role of Ras proteins in growth control in many species and in neoplasia in humans (Barbacid, 1987) . The Ras protein sequence is highly conserved throughout eukaryotes and mammalian RAS genes are functional in yeast. Also, mutated yeast RAS genes efficiently transform mouse fibroblast cell lines. Of particular interest is the ability of p48 to suppress the heat shock sensitivity of yeast strains containing a Ras mutation. See, for an example of this function, Example IV, infra . Further studies are required to delineate the exact functional interactions between Rb, p48, p46 and Ras in mammalian cells, however, it is obvious in light of the present disclosure, that the polypeptide and nucleic acid compounds and sequences of the present invention have tremendous utility in increasing the understanding of tumorigenesis and growth and development of healthy human cells.

Isolation of Rb Binding Proteins

Binding of viral proteins to the Rb gene product has inspired a search for cellular binding partners of this important tumor suppressor. Several methods have been shown to be effective in isolating Rb binding proteins. One approach to isolating such proteins is to purify them from cell extracts with Rb protein affinity columns. Example I, infra, provides an example of the preparation and use of an Rb affinity column in the isolation of p48 in the present invention.

Briefly, affinity chromatography is based on the recognition of a protein by a substance such as a ligand or an antibody. The column material is synthesized by covalently coupling a binding molecule, such as a protein, for example to an insoluble matrix. The column material is then allowed to adsorb the desired substance from solution and then the conditions are changed to those under which binding does not occur and the substrate is eluted. The requirements for successful affinity chromatography are that the matrix must not adsorb the target molecules, the ligand must be coupled without altering its binding activity, a ligand must be chosen whose binding is sufficiently tight, and it must be possible to elute the substance without destroying it.

Often, the ligand which is immobilized is a protein which binds a substance, another protein for example, or an antibody that recognizes a particular protein. Various materials are available for immobilizing ligands. Some examples are cyanogen bromide activated agarose, 6- aminohexanoic acid and 1,6 diaminohexane-agarose, epoxy activated agarose, thiopropyl agarose, carbonyldiimidazole activated agarose, and aminoethyl and hydrazide activated polyacrylamide (Freifelder, 1982) . While affinity chromatography is a preferred method of isolating p48 from cellular extracts, other ways of purifying the protein exist including those delineated below. It is understood that p48 purified or identified by any of the following methods, or any equivalent methods is encompassed by the present disclosure.

Another approach is to directly test good candidate proteins for their ability to bind the Rb gene product. For example c-myc, N-myc, E2F, ATF-2, and cdc2 proteins are capable of binding Rb protein in vitro. All of these proteins require a carboxyl terminal region of Rb that includes the domain required for binding to the DNA tumor virus transforming proteins. However, these proteins seem to require additional carboxyl terminal sequences that are not required for SV40 T antigen binding.

One preferred method to determine direct binding of two proteins is based on the gel mobility of the proteins. The mobility through a polyacrylamide gel can be determined for each protein individually. The proteins are then mixed and allowed to interact in solution. The mobility of the mixture of the two proteins can be compared to their individual mobilities through separate lanes in a gel matrix under non- denaturing conditions. The appearance of a new, more slowly migrating protein species when the two proteins are mixed indicates binding. The slower migrating species can then be isolated and subjected to SDS-PAGE, during which the two proteins will separate, confirming that the complex is formed of the correct proteins. Proteins cans be visualized by standard methods such as silver staining or coomassie blue dye, for example.

A third possible method for identifying cellular, Rb associated proteins is to screen lambda expression libraries using purified Rb protein as a probe. Several novel genes of unknown function have been identified by this method, and one gene which encodes a protein with properties similar to the transcription factor E2F (Shan et al . , 1992; Helin et al . , 1992; Kaelin et al . , 1992) .

Another technique used to isolate Rb associated proteins involves a yeast two-hybrid transcription factor screening system (Chien et al . , 1991) . Briefly, the Gal4 DNA binding domain is fused to the putative binding domain of Rb. The resulting fusion protein can bind DNA at a GA14 binding sequence, but cannot activate a GA14 dependent promoter since the Gal4 activation domain has been replaced by Rb. A lambda library is constructed that fuses random cDNAs to the transactivation domain of Gal4. If a cDNA encodes a protein that associates with Rb protein, then the Gal4 transactivation domain will be brought into proximity of the DNA binding domain thereby activating transcription from the Gal4 dependent promoter. Activation of the Gal4 dependent promoter serves as the basis for selection and/or screening of the cDNA clones. One advantage of this system, is that binding is detected in a living cell .

T Antigen

SV40 T antigen, or a T antigen derived peptide can compete for binding to Rb protein with some cellular proteins, and in particular with p48 binding. The T antigen binds to specific sites in the SV40 DNA sequence and inhibits transcription initiation from the early SV40 promoter. The large T antigen of SV40 complexes preferentially with the underphosphorylated form of the Rb gene product, implying that the underphosphorylated form may be the biologically active form (Ludlow et al . , 1989) . It is possible that DNA tumor viruses induce transformation by binding the active form of the Rb protein, thereby inhibiting its normal, suppression function (Dyson et al . , 1989b) . In the process of constructing transgenic mice with SV40 large T antigen under the control of a tissue-specific promoter, a particular line of mice has been identified that expressed large T in the developing retina (Windle et al . , 1990) . These mice reproducably develop a neoplasm of the eye that is histologically related to human retinoblastoma. The apparent correlation between tumorigenicity of a iral strain, the ability of its protein to complex with the Rb gene product, and the induction of retinoblastoma by T antigen suggests that binding of Rb to these viral proteins may have biological relevance. It is also significant that the p48 protein of the present invention competes with T antigen binding to the Rb protein and thus interacts with what is believed to be a biologically important region of Rb.

MSI1

In the yeast Saccharomyces cerevisiae, the signal transduction for growth in response to nutrients is mediated by the RAS-cAMP pathway (Tatchell, K. , 1986) . The yeast RAS proteins play an important role in this process by activating adenylate cyclase, which induces the formation of cAMP (Toda et al . , 1985; Broek et al . , 1985) . The levels of this second messenger regulate, by means of cAMP-dependent protein phosphorylation, the progression of the cell cycle through the early G_j phase (Matsumote et al . , 1985) . The ras proteins are highly conserved in evolution (Barbacid, M. , 1987) . The extended structural homology between the yeast and the mammalian ras proteins suggests that they may serve a fundamental function in cellular proliferation. Mutations in mammalian ras proteins have been associated with cell transformation (Barbacid, M. , 1987) . Interestingly, the analogous alteration in the yeast RAS2 sequence (RAS2^Va"⁹) causes defects in the cell cycle control exerted by nutrients (Toda et al . , 1985) .

IRAl , a gene whose product negatively regulates the RAS-cAMP pathway has been identified (Tanaka et al . , 1989) . Genetic evidence indicates that this protein may operate on RAS proteins in a manner opposite to the function of the CDC25 protein. IRAl gene disruption can suppress the lethality of the cdc25 mutation and causes an increased level of intracellular cAMP (Tanaka et al . , 1989) . These phenotypes are typical of the RAS2^VαiI9 mutant, which has a reduced intrinsic GTPase activity (Broek et al . , 1985) . These observations, together with its partial homology to mammalian GAP (GTPase activating protein) (Voegl et al . , 1988) , suggest that IRAl acts to down-regulate RAS activity, and hence adenylate cyclase, by stimulating the GTPase activity of RAS proteins. A suppressor gene of the heat shock sensitive phenotype caused by the viral mutation has also been isolated (Ruggieri et al . , 1989) . This suppressor gene, MSIl , negatively regulates the cAMP level in response to glucose.

RbAp48 shares sequence homology with MSIl . Furthermore, like MSIl , human RbAp48 suppresses the heat shock sensitivity of the yeast iral strains and RAS2*^α"⁹ strains. Therefore, p48 may provide a link between the heat shock response in yeast and viral transforma- tion/oncogenesis that is known to involve Rb. In the heat shock experiments, yeast are grown in YPD medium (2% Bacto peptone, 1% Bacto yeast extract, and 2% glucose; or SD medium (.67% yeast nitrogen base without amino acids, 2% glucose) , or SD medium supplemented with auxotrophic requirements. Fresh cells are grown at 25°C and treated for example, for 20 minutes at 57°C or 1 hour at 50°C to induce heat shock. The cells may then be cooled on ice and incubated for about 48 hours at 25°C.

p53 and Heat Shock Proteins

The viral transforming proteins also bind other cellular proteins that may be important in tumorigenesis, including p53 (Linzer and Levine, 1979) . Wild type p53 is another tumor suppressor which is frequently found to contain mutations in tumor cells, and that loss of normal p53 expression may be an important step in cell transformation and tumorigenesis (Montenarh, 1992) . It is known that the p53 tumor suppressor gene can bind to the heat shock protein/heat shock cognate, 72hsp/73hsc, and that a mutant from of p53 is more firmly associated. It has also been demonstrated that Rb binds to the nuclear heat shock cognate 73hsc (Nihei et al. , 1993). Although the biological significance of the association between p53 and heat shock proteins in the oncogenic process is not yet known, it is suggested that these protein associations may play ah important role in oncogenesis (Scheffner et al . , 1990). This interaction adds another layer of regulation of cell growth and proliferation in which the Rb protein and its effectors are involved. It is essential to understand this pathway of cellular control in order to be able to control tumorigenesis and the discovery of the present invention is an important step in that process of understanding. Nucleic Acid Hybridization

In addition to their use in directing the expression of the p48 and p46 proteins, the nucleic acid sequences disclosed herein also have a variety of other uses. For example, they also have utility as probes or primers in nucleic acid hybridization embodiments. Oligonucleotide fragments corresponding to the sequence of SEQ ID NO:l for stretches of between about 10 to 15 nucleotides and about 20 to 30 nucleotides will have utility, as wili longer complementary sequences, e.g., those of about 40,, 50, 100, 200, 500, 1000, and even up to full length sequences of about 2291 nucleotides in length.

The use of a hybridization probe of about 10 nucleotides in length allows the formation of a duplex molecule that is both stable and selective. Molecules having complementary sequences over stretches greater than 10 bases in length are generally preferred, though, in order to increase stability and selectivity of the hybrid, and thereby improve the quality and degree of specific hybrid molecules obtained. One will generally prefer to design nucleic acid molecules having gene- complementary stretches of 15 to 20 nucleotides, or even longer where desired. Such fragments may be readily prepared by, for example, directly synthesizing the fragment by chemical means, by application of nucleic aid reproduction technology, such as the PCR technology of U.S. Patent 4,603,102 (herein incorporated by reference) or by introducing selected sequences into recombinant vectors for recombinant production.

Accordingly, the nucleotide sequences of the invention may be used for their ability to selectively form duplex molecules with complementary stretches of p46 or p48 genes or cDNAs . Depending on the application envisioned, one will desire to employ varying conditions of hybridization to achieve varying degrees of selectivity of probe towards target sequence. For applications requiring high selectivity, one will typically desire to employ relatively stringent conditions to form the hybrids, e.g., one will select relatively low salt and\or high temperature conditions, such as provided by 0.02M-0.15M NaCI at temperatures of 50°C to 70°C. Such selective conditions tolerate little, if any, mismatch between the probe and the template or target strand, and would be particularly suitable for isolating p48 and p46 genes.

Of course, for some applications, for example, where one desires to prepare mutants employing a mutant primer strand hybridized to an underlying template or where one seeks to isolate p48 or p46-encoding sequences from related species, functional equivalents, or the like, less stringent hybridization conditions will typically be needed in order to allow formation of the heteroduplex. In these circumstances, one may desire to employ conditions such as 0.15M-0.9M salt, at temperatures ranging from 20°C to 55°C. Cross-hybridizing species can thereby be readily identified as positively hybridizing signals with respect to control hybridizations. In any case, it is generally appreciated that conditions can be rendered more stringent by the addition of increasing amounts of formamide, which serves to destabilize the hybrid duplex in the same manner as increased temperature. Thus, hybridization conditions can be readily manipulated, and thus will generally be a method of choice depending on the desired results.

In certain embodiments, it will be advantageous to employ nucleic acid sequences of the present invention in combination with an appropriate means, such as a label, for determining hybridization. A wide variety of appropriate indicator means are known in the art, including fluorescent, radioactive, enzymatic or other ligands, such as avidin/biotin, which are capable of giving a detectable signal. In preferred embodiments, one will likely desire to employ a fluorescent label or an enzyme tag, such as urease, alkaline phosphatase or peroxidase, instead of radioactive or other environmental undesirable reagents. In the case enzyme tags, colorimetric indicator substrates are known which can be employed to provide a means visible to the human eye or spectrophotometrically, to identify specific hybridization with complementary nucleic acid-containing samples.

In general, it is envisioned that the hybridization probes described herein will be useful both as reagents in solution hybridization as well as in embodiments employing a solid phase. In embodiments involving a solid phase, the test DNA (or RNA) is adsorbed or otherwise affixed to a selected matrix or surface. This fixed, single-stranded nucleic acid is then subjected to specific hybridization with selected probes under desired conditions. The selected conditions will depend on the particular circumstances based on the particular criteria required (depending, for example, on the G+C contents, type of target nucleic acid, source of nucleic acid, size of hybridization probe, etc.) . Following washing of the hybridized surface so as to remove nonspecifically bound probe molecules, specific hybridization is detected, or even quantified, by means of the label.

Detection of Mutations in the p46 and p48 Genes

The DNA sequences of the present invention will find use as probes for detecting mutations in the p46 and p48 genes in the diagnosis and prognosis of certain tumors. Two preferred methods of discovering these mutations are SSCP (single strand conformation polymorphism) and ribonuclease protection assays. The former is based on the understanding that mutations within a DNA molecule will cause that molecule to migrate at a different rate through a denaturing gradient gel such as a polyacrylamide containing a gradient of formamide and urea. The sample DNA is allowed to hybridize to the control (wild type) DNA and then is loaded into the gradient gel. The mutation will cause the duplex to be less stable than a perfectly matched duplex and hence will melt at a lower concentration of urea and formamide. This sample is run in an adjacent lane to a known perfectly matched duplex, such as the double stranded form of the sequences disclosed herein.

Another preferred method is the ribonuclease protection assay. This reaction is typically done with RNase A, which cleaves single stranded RNA preferentially over double stranded RNA. Again, a control, perfectly matched duplex, this time involving at least one strand of RNA is reacted with RNase simultaneously with a sample which may contain one or more mutations, hybridized to the wild type p46 or p48 RNA segment, for example. The RNase will preferentially cleave the RNA at the point of a mismatch, due to the single stranded nature of the duplex at the mismatch. By comparing the fragment size of the control vs. the sample RNA products of this reaction, mutations can be detected. The products can be separated on an agarose gel, for example, and visualized by ethidium bromide staining.

Mutations that affect expression of p46 or p48 in a particular cell may also be detected by immunoprecipi- tating the proteins from sample cell lysates. In their most simple and direct sense, immunoprecipitation allows the determination of the presence or absence of the particular protein in the lysates of cells. For an example of immunoprecipitation, see Example III, infra . Another preferred method of detecting p48 or p46 proteins with mutations that affect the conformation of immunoreactivity or the proteins is by Western blotting. Briefly, cells may be harvested, pelleted and dissolved in lysis buffer (50 mM Tris-HCI, 5% β-mercaptoethanol, 2% sodium dodecyl sulfate, 0.1% bromophenol blu, 10% glycerol) . Proteins of cell lysates are then separated by polyacrylamide gel electrophoresis in reducing conditions. The gel is then contacted by a nitrocellulose filter, for example and the proteins are transferred to the filter by electroelution, for example. The filters are then incubated in phosphate buffered saline containing 5 bovine serum albumin, washed and incubated with the primary antibody to p46 or p48, washed and then incubated with peroxidase-conjugated goat anti- human IgG secondary antibody (Boehringer Mannheim) . The filters are again washed and the color forming reaction is performed using 4-chloro-l-napthol in methanol with H2O2, for example.

Biological Functional Equivalents

As mentioned above, modification and changes may be made in the structure of p46 or p48 and still obtain a molecule having like or otherwise desirable characteristics. For example, certain amino acids may be substituted for other amino acids in a protein structure without appreciable loss of interactive binding capacity with structures such as, for example, protein-binding regions of other molecules. Since it is the interactive capacity and nature of a protein that defines that protein's biological functional activity, certain amino acid sequence substitutions can be made in a protein sequence (or, of course, its underlying DNA coding sequence) and nevertheless obtain a protein with like or even countervailing properties (e.g., antagonistic v. agonistic) . It is thus contemplated by the inventors that various changes may be made in the sequence of p46 or p48 proteins or peptides (or underlying DNA) without appreciable loss of their biological utility or activity.

In making such changes, the hydropathic index of amino acids may be considered. The importance of the hydropathic amino acid index in conferring interactive biologic function on a protein is generally understood in the art (Kyte & Doolittle, 1982, incorporated herein by reference) . It is accepted that the relative hydropathic character of the amino acid contributes to the secondary structure of the resultant protein, which in turn defines the interaction of the protein with other molecules, for example, enzymes, substrates, antibodies, DNA and the like.

Each amino acid has been assigned a hydropathic index on the basis of their hydrophobicity and charge characteristics (Kyte & Doolittle, 1982), these are: isoleucine (+4.5) ; valine (+4.2) ; leucine (+3.8) ; phenylalanine (+2.8); cysteine/cystine (+2.5) ; methionine (+1.9) ; alanine (+1.8) ; glycine (-0.4) ; threonine (-0.7) ; serine (-0.8) ; tryptophan (-0.9) ; tyrosine (-1.3) ; proline (-1.6) ; histidine (-3.2) ; glutamate (-3.5) ; glutamine (-3.5) ; aspartate (-3.5) ; asparagine (-3.5) ; lysine (-3.9) ; and arginine (-4.5) .

It is known in the art that certain amino acids may be substituted by other amino acids having a similar hydropathic index or score and still result in a protein with similar biological activity, i.e., still obtain a biological functionally equivalent protein. In making such changes, the substitution of amino acids whose hydropathic indices are within ±2 is preferred, those which are within ±1 are particularly preferred, and those within ±0.5 are even more particularly preferred. It is also understood in the art that the substitution of like amino acids can be made effectively on the basis of hydrophilicity, particularly where the biological functional equivalent protein or peptide thereby created is intended for use in immunological embodiments. U.S. Patent 4,554,101, incorporated herein by reference, states that the greatest local average hydrophilicity of a protein, as governed by the hydrophilicity of its adjacent amino acids, correlates with its immunogenicity and antigenicity, i.e. with a biological property of the protein.

As detailed in U.S. Patent 4,554,101, the following hydrophilicity values have been assigned to amino acid residues: arginine (+3.0) ; lysine (+3.0) ; aspartate

(+3.0 ± 1); glutamate (+3.0 ± 1); serine (+0.3); asparagine (+0.2); glutamine (+0.2) ; glycine (0) ; threonine (-0.4) ; proline (-0.5 + 1); alanine (-0.5); histidine (-0.5) ; cysteine (-1.0) ; methionine (-1.3) ; valine (-1.5); leucine (-1.8) ; isoleucine (-1.8) ; tyrosine (-2.3) ; phenylalanine (-2.5) ; tryptophan (-3.4) .

It is understood that an amino acid can be substituted for another having a similar hydrophilicity value and still obtain a biologically equivalent, and in particular, an immunologically equivalent protein. In such changes, the substitution of amino acids whose hydrophilicity values are within ±2 is preferred, those which are within +1 are particularly preferred, and those within ±0.5 are even more particularly preferred.

As outlined above, amino acid substitutions are generally therefore based on the relative similarity of the amino acid side-chain substituents, for example, their hydrophobicity, hydrophilicity, charge, size, and the like. Exemplary substitutions which take various of the foregoing characteristics into consideration are well

methods . Hybridoma clones can then be cultured in liquid media and the culture supernatants purified to provide the p46 or p48-specific monoclonal antibodies.

In general, both poly- and monoclonal antibodies against p46 or p48 may be used in a variety of embodiments. For example, they may be employed in antibody cloning protocols to obtain cDNAs or genes encoding p46 or p48 from other species or p46 or p48-like proteins. A particularly useful application of such antibodies is in purifying native or recombinant p46 or p48, for example, using an antibody affinity column. The operation of all such immunological and cloning techniques will be known to those of skill in the art in light of the present disclosure.

Anti-p46 or p48 antibodies may also be used in inhibition studies to analyze the effects of p46 or p48 in cells or animals. Anti-p46 or p48 antibodies will also be useful in immunolocalization studies to analyze the distribution of p46 or p48 during various cellular events, for example, during the cell cycle or during the processes of viral infection of tumorigenesis in cultured cells.

It is proposed that anti-p46 or p48 antibodies will also find useful applications in analyzing the distribution of p46 or p48 throughout the human body, and especially in patients with various cancers such as retinoblastoma. The antibodies may be used to detect p46 or p48, such as in determining p46 or p48 levels. Alternatively, native- or mutant-specific antibodies may be prepared and used to detect native or mutant p46 or p48, to gain qualitative information on p46 or p48 in different patients. Any such anti-p46 or p48 antibodies may be used to detect p46 or p48 species in connection with standard immunochemical procedures, such as immunohistochemical, ELISA and Western blot methods.

The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

EXAMPLE I

The gene encoding RbAp48 or p48, the retinoblastoma binding protein was cloned from a human HeLa cell cDNA library. The DNA sequence encoding the protein was determined and the deduced amino acid sequence was found to exhibit homology to the Msil amino acid sequence.

Cloning the RbAp48 gene

Several cellular proteins, including E2F, have been shown to interact with the carboxyl terminus of the Rb protein, p56^Rb (Lee et al . , 1991; Huang et al . , 1991; DeFeo-Jones et al . , 1991; Kaelin et al . , 1991; Kaelin et al . , 1992; Helin et al . , 1992; Shan et al . , 1992) . At least nine proteins in HeLa cell lysates or retinoblastoma cell line Weri-24 cell lysates were specifically absorbed to a p56^Rb column (Lee et al . ,

1991; Kaelin et al . , 1991) . This binding was abolished by pre-incubation of the column with T peptide, a syntectic 18-amino acid polypeptide containing residues 101-118 of T antigen, but not by pre-incubation with K peptide, a mutant version of T peptide (DeCaprio et al . , 1989) (Fig. IA) . Competition for binding was also seen with purified T antigen. These results not only indicate the specificity of the interaction between the nine cellular proteins and Rb, but also suggest that the T- binding domains of Rb may be involved in the interaction. The original designation of p46 (Lee et al . , 1991) has been changed to p48 and as illustrated in Fig. IA. p48 in Fig. IA has a similar but distinct electrophoretic mobility relative to the common protein cl.

A strategy involving microsequencing of purified p48, design of oligonucleotide probes from the partial amino acid sequence, and PCR amplification was employed in the isolation of complementary DNA clones encoding p48. Sequencing of the largest insert revealed a single open reading frame of 425 amino acids with a predicted molecular mass of 47.6 kDa. The two polypeptide sequences obtained from microsequencing of the isolated protein were present within the amino acid sequence deduced from the putative open reading frame. The predicted amino acid sequence of RbAp48 was compared with sequences in GenBank (version 71) and was found to exhibit significant homology with the putative amino acid sequence of the yeast S. cerevisiae MSIl gene. Msil is presumably a negative regulator in the Ras-cAMP pathway in the yeast S. cerevisiae, since overexpression of the MSIl gene suppresses the heat shock sensitivity of

RAS2^Vαl19 and iral mutants, and reduces the cAMP level in these mutants (Ruggieri et al . , 1989) . The predicted p48 and Msil amino acid sequences share 30% identity (46% similarity) over their entire lengths. Interestingly, internal repeats, which were first identified in the transducin b subunit (Fong et al . , 1986) , are present in both p48 and Msil proteins. Methods

p56^Rb was expressed in E. coli as previously described (Huang et al . , 1991) except that IPTG induction was performed at 30°C for 3 h. p56^Rb affinity matrixes were produced by the cross-linking of approximately 1 mg of purified p56^Rb to 1 ml (bed volume) of Affi-Gel 10 resin (Bio-Rad) according to the manufacturer's instructions. HeLa cells, 1x10 , were lysed in 10 ml EBC buffer (50 mM Tris-HCI, pH 8.0, 120 mM NaCI, 0.5% Nonidet P-40, 1 mM /3-mercaptoethanol, 1 mM EDTA, 200 U ml^"1 aprotinin, 200 U ml^-1 leupeptin, 1 mM PMSF, lmM NaF) . The lysate was clarified by centrifugation at 35,000 r.p.m. for 30 min at 4°C followed by filtration using 0.45 mm filter.

For binding competition, 100 ml of Rb matrices were first incubated with 0.5 ml EBC buffer containing 0.3 mM T peptide or K peptide for lh at 4°C followed by the addition of 1 ml lysate and further incubation at 4°C for 1 h. The amino-acid sequence of T peptide is ENLFCSEEMPSSDDEAAT (SEQ ID NO:3) , and K peptide is ENLFCSKEMPSSDDEAAT (SEQ ID NO:4) . After extensive washing with NET buffer (50 mM Tris-HCI, pH 8.0, 0.2 M NaCI, 1 mM EDTA, 1 mM 0-mercaptoethanol, 1 mM PMSF, 1 mM NaF) , bound proteins were released from matrixes using 2-D sample buffer (1.2g urea, 100 ml ampholines, pH 3.5-10, 400 ml 10% NP-40, 20 ml 3-mercaptoethanol, 680 ml H2O) and resolved by isoelectric focusing in a pH 3.5- 10.0 gradient containing 155 ml of pH 3.5-10.0 ampholine (LKB) with 310 ml of pH 5.0-7.0 ampholine (LKB) per 10 ml of gel solution followed by fractionation using SDS polyacrylamide gel electrophoresis (Lee et al . , 1991) .

Proteins were visualized by silver staining (Fig. IA) . For amino acid sequencing, coomassie-blue stained gel pieces containing about 20 mg of p48 were collected from 2-D gels and digested with CNBr in si tu . The resultant peptides were separated in a 15% SDS- polyacrylamide gel and transferred onto a polyvinylidene difluoride (PVDF) membrane (Millipore) according to

Matsudaira (1989). The membrane was stained with 0.1% Coomassie blue in 50% (v/v) methanol for 5 min and washed with water. Pieces of membrane containing CNBr fragments were used directly for microsequencing. Two peptide sequences (underlined in Fig. IB) were obtained.

Two degenerate oiigonucleotides were synthesized for the polymerase chain reaction (PCR) using first strand cDNA synthesized from fetal brain RNA templates. The forward PCR primer was GAR GAY ACH GTB GAR GAR MG (SEQ ID NO:7) ; the reverse PCR primer was GTR TTY TTY TTC CAR ATY TTR TA (SEQ ID NO:8) . The PCR reaction was carried out in a reaction mixture containing 4 μg forward primer, 4 μg reverse primer, and 1 U Tag polymerase (Perkin-Elmer- Cetus) . Amplification conditions were 30 cycles of 93°C for 1 min, 50°C for 1 min and 72°C for 1 min. This reaction generated one band of 60 basepairs (bp) which was subcloned, sequenced and shown to encode the previously determined peptide sequences. A HeLa cell Lambda gtll cDNA library was then screened with the 60 bp fragment. Of ~8.2xl0⁵ bacteriophage screened, thirteen bacteriophage contained inserts that hybridized with the oligonucleotide probe in a Southern blot analysis.

EXAMPLE II

In order to determine whether the gene isolated from the cDNA library encodes the protein isolated from the affinity column, comparisons were made based on the size and immunogenicity of the isolated and the recombinant proteins . RbAp48 encodes p48

To further confirm that the cDNA clone encodes p48, the protein was overexpressed in E. coli and antibodies were raised against the putative p48 purified from the bacteria. These polyclonal antibodies recognize authentic p48 and p46 in the Rb-affinity column eluates. In addition, monoclonal antibodies that recognize p48 were produced. Several monoclonal antibodies including 13D10 recognized only one protein in the Rb-affinity column eluates (Fig. 2C, right panel) . The immunoreactive protein co-localizes with p48 in the autoradiograph of the 2-D gel in Fig. 2C, left panel. Based on the sequence analysis and the immunological data, it is the inventors' conclusion that RbAp48 encodes p48.

Methods

The unmodified RbAp48 transcript was synthesized using T7 RNA polymerase, and a Kpn I linearized pGEM- RbAp48 plasmid template containing a 2.2 kb RbAp48 cDNA fragment inserted into the EcoR I site of the vector pGEM-3Z. The chimeric RbAp48 transcript was synthesized using SP6 RNA polymerase, and an EcoRI linearized pb- RbAp48 plasmid that contains the RbAp48 coding region inserted into the Ncol-EcoRI sites of the plasmid pBlO (Huang et al . , 1990). The resulting capped transcripts were translated in reticuiocyte lysates according to the manufacturer's instructions (Promega) . Protein products were separated by SDS-PAGE directly or were immunoprecipitated with anti-p48 monoclonal antibody 13D10 prior to loading.

A 5 ml aliquot of the translation product using pb- RbAp48 as the template was resuspended in 0.3 ml EBC buffer, and mixed with 15 ml of 13D10 (100 mg ml^" on ice for lh. Fifty microliters of protein G-Sepharose beads in EBC containing 4% BSA was added and the mixture was rocked at 4°C for lh. The beads were subsequently washed once with EBC buffer, three times with EBC buffer containing 1 M NaCI, and once again with EBC buffer.

Five microliters of translation products in the absence of RNA or in the presence of RNA from pGEM -RbAp48, and 1 ml translation product with RNA from pb-RbAp48 were analyzed on a 10% SDS-polyacrylamide gel. The resulting fluorographs are shown in Fig. 2A.

A comparison of the affinity chromatography eluted protein and the in vi tro translation product is shown in Fig. 2B. Eluates were prepared as described in Fig. 1 except bound proteins were released from matrices by boiling in SDS sample buffer for 5 min. Eluates, and 1 ml of the translation product of RNA from τpb-RbAp48 were separated on a 10% SDS-polyacrylamide gel and transferred onto a PVDF membrane by standard techniques. The membrane was first incubated with blocking buffer, then monoclonal antibody 13D10, followed by alkaline phosphatase-conjugated goat anti-mouse IgG.

Rb matrices were incubated with lysates from 5x10" cells labeled with ³⁵S-methionine and lxlO⁸ unlabelled HeLa cells. Bound proteins were separated in a 2-D gel and incubated with antibody 13D10 (Fig. 2C, right panel) . The filter was then visualized by fluorography (Fig. 2C, left panel) .

EXAMPLE III

The interaction between p48 and Rb protein was studied by several different approaches. First, purified p48 and p56^Rb were incubated together prior to the addition of anti-Rb polyclonal antibodies. p48 was co- immunoprecipitated by anti-Rb antibody 0.495 (Wang et al., 1990) . Second, binding of p48 and Rb was examined in vivo using tumor cell lines with and without Rb mutations.

In vivo and in vitro interaction of Rb and p48

In co-immunoprecipitation experiments with anti-Rb antibody, p48 was co-precipitated with Rb in cells expressing wild-type Rb (HeLa and Molt-4; Fig. 3A, lanes 1 & 6) but not in cells that lack Rb due to a complete deletion of the gene (Fig. 3A, lane 2) , nor in cells known to have deletions within the T-binding domains of Rb (Fig. 3A, lanes 3-5) . p48 is present in all the cell types used in this study. In similar experiments with anti-p48 antibody, only unphosphorylated and hypophosphorylated forms of the Rb protein were co- precipitated with p48 (Fig. 3A, lanes 8 & 9) . The in vivo association of Rb with p48 was also demonstrated by sequential lmmunoprecipitations with ^JJS-methionine labeled cells. As shown in Figure 3B, anti-p48 antibody 13D10 specifically recognized p48 present in immune complexes formed with anti-Rb antibody 0.495 (Fig. 3B, left panel) . Conversely, anti-Rb antibody 0.495 specifically re-immunoprecipitated only the unphosphorylated and hypophosphorylated forms of Rb protein from immune complexes formed with anti-p48 antibody 13D10 (Fig. 3B, right panel) .

It was also contemplated that p48 may interact directly with Rb. Under appropriate conditions, p48 and p56^^u each migrated as a single broad band on a non- denaturing polyacrylamide gel (Fig. 3C) . When the two proteins were incubated together prior to electrophoresis, a new protein band was identified (Fig. 3C, left panel) . This new band contains p48-Rb complexes, as shown by excision of the band followed by separation of the individual proteins by SDS polyacrylamide gel electrophoresis (Fig. 3C, right panel) . Similarly, complexes are formed between p48 and full-length Rb. Since Rb is a nuclear protein (Lee et al . , 1987) , it is expected that interaction between p48 and Rb takes place in the nucleus. Subcellular fractionation and immunocytochemistry studies done by the inventors demonstrate that p48 is also a nuclear protein.

Methods

Whole cell lysates were prepared as described in Fig. 1. The lysates were incubated with the appropriate antibodies on ice for lh. Fifty microliters of protein G-Sepharose beads in EBC containing 4% BSA were added and the mixtures were rocked at 4°C for 2h. The beads were subsequently washed three times with NET buffer, and twice with EBC buffer. The resulting immune complexes were released from the beads by boiling in SDS sample buffer for 10 min and then analyzed by immunoblotting (Fig. 3A) .

The first immunoprecipitation was carried out as described above. The resulting immune complexes were boiled in the presence of 2% SDS to dissociate protein complexes according to Helin et al . (1992) . The denatured proteins were diluted 25-fold with EBC buffer containing 3 mg ml^"1 BSA and re-immunoprecipitated with additional antibody as indicated. The beads were subsequently washed three times with EBC buffer containing 1 M NaCI, and twice with EBC buffer. The resulting immune complexes were dissociated from the beads by boiling in SDS sample buffer and separated in a 10% SDS-polyacrylamide gel. The proteins were visualized by fluorography (Fig. 3B) .

The Ncol-BamHI fragment of p48 cDNA was inserted into the Ncol and BamHI sites of pET8c vector (Studier et al . , 1990) . The resulting plasmid pET-48NB encodes a chimeric p48 protein containing a modified C-terminus (five C-terminal amino-acids of p48, EGQGS (SEQ ID N0:5) , were replaced by eighteen amino-acids, AANKARKEAELAAANAEQ, SEQ ID NO:6) . This plasmid was transformed into the host cell, BL21 (DE3) pLysS and transformants were grown to a OD^QQ of 0.6-1.0 at 37°C in LB media containing 100 mg ml^"1 ampicillin and 25 mg ml^"1 chloramphenicol . The growth temperature was reduced to 30°C, and IPTG was added to a final concentration of 0.4 mM. The bacteria were collected 3 h later and lysed in EBC buffer by freezing, thawing, and sonicating. The inclusion body was collected by centrifugation at 10,000 r.p.m. for 10 min. The pellet was extensively washed with EBC buffer. The washed inclusion body was dissolved in 8 M urea and then successively dialyzed against 6 M urea, 4 M urea, 2 M urea, 1 M urea, and finally in renaturation buffer (0.2 M Tris-HCI, pH 8.0, 0.5 M NaCI) for 12 h. The refolded protein was further purified by gel filtration using a Sephacryl S-300 column equilibrated with S-300 buffer (20 mM sodium phosphate, pH 7.5, 200 mM NaCI, 1 mM EDTA, 1 mM jS-mercaptoethanol, 10% glycerol) . Half microgram of p56^Rb, 0.2 mg of p48, and a mixture of both in 5X Tris-Glycine buffer (0.125 M Tris-Glycine, pH 8.8) were separated on a 6% native- polyacrylamide gel. Electrophoresis was carried out in IX Tris-Glycine buffer (See Fig. 3C) .

EXAMPLE IV

Because of the similarity between the putative amino acid sequences of p48 and Msil, the ability of a cDNA encoding p48 to suppress the heat shock sensitivity of the two yeast mutant strains, RAS2^Vα^⁹ (TK161-R2V) , and iral (KT6-1A-D) was tested. Heat shock suppression by p48

Introduction of either pd3, the yeast MSI-containing plasmid, or pd3::p48, but not control plasmid YEp24 conferred complete resistant to heat shock (Fig. 4) . YEp24-transformed and untransformed KT6-1A-D cells did grow slightly after heat shock presumably due to the low level heat shock resistance of the iral mutant strain (Ruggieri, personal communication) . However, the survival level was well below that of the cells that were transformed with the MSI and p48 containing plasmids.

To confirm that heat shock resistance was due to the pd3:.-p48 plasmid itself, plasmid loss analyses were performed. These analyses demonstrated that all transformants that lose the pd3::p48 plasmid no longer survive heat shock. In addition, similar results were obtained using the pYC: :p48 in which the RbAp48 gene is transcribed under the control of the strong yeast ADH1 promoter. Although the mechanism of heat shock resistance is unknown, these data provide evidence that RbAp48 is functional in yeast, and p48 mimics the function of Msil in yeast.

Methods

Strains TK161-R2V (Λ-ATa RAS2^Vαl19 leu2 ura3 trpl his3 ade8 canl) and KT6-1A-D {MATa/MATa iral : :LUE2/ iral : :LEU2 ura3/ura3 Ieu2/leu2 trpl/trpl his3/his3) and plasmid pd3 (MSIl URA3) (Ruggieri et al . , 1989) were kindly provided by R. Ruggieri. Plasmid pd3::48K was constructed by replacing the Clal -Xho I coding region of the MSIl gene on pd3 with the Neo I -Kpn I coding region of the RbAp48. This yielded an in-frame fusion between MSIl codon 17 and RbAp48 codon 1, effectively substituting the entire open reading frame for that of MSIl . This plasmid, as well as pd3 and control vector YEp24 were transformed into each of the yeast strains by the spheroplast method (Sherman et al . , 1986). Transformants were patched onto selective medium plates, and after one day of growth at 30°C, were replica-plated onto two rich medium plates. One of these plates was incubated for two days at 30°C, while the other was heat-shocked by incubation at 57°C for 20 min (TKK161-R2V) or 30 min (KT6-1A-D) prior to incubation for 2 days at 30°C. The longer heat shock period was used for KT6-1A-D since this strain is known to be partially resistant to heat shock, possibly due to occasional reversion of the iral : :LEU2 insertion.

EXAMPLE V

A gene encoding p46, the retinoblastoma binding protein has also been cloned from a human HeLa cell library. The nucleic acid sequence of the gene has been determined and the deduced amino acid sequence compared to the p48 amino acid sequence. The amino acid sequences share a 95% homology, but significant differences exist in the 5' and 3' untranslated regions, indicating that these two proteins are encoded by different genes.

Cloning the RbAp46 gene

Polyclonal and monoclonal antibodies to the p48 protein were found to crossreact with the p46 protein in a Western Blot analysis. One of these monoclonal antibodies was chosen to screen a lambda gtll expression library created from human HeLa cells for a clone expressing the p46 protein. A full-length cDNA was isolated by this method. Sequence analysis revealed a 425 amino acid open reading frame which shares a 95% amino acid homology with p48 as seen in Figure 6. EXAMPLE VI

It is contemplated that p46 or p48 will have utility in suppressing the oncogenic p21 RAS in human tumor cells. RAS point mutations have been found in diverse tumor types ranging from leukemias to colorectal carcinomas. The Ras signal pathway is believed to be highly conserved in eukaryotic organisms. The inventors have demonstrated that p46 or p48 can suppress the heat shock phenotype in a yeast strain carrying a RAS mutation (See Example IV, infra) . It is therefore plausible that overexpression of p46 or p48 can suppress the activity of oncogenic RAS in mammalian cells.

Use of p46 or p48 in Treatment of Human Tumors

Preliminary findings indicate that the level of expression of p48 or p46 is important in their biological function. Therefore, it is contemplated that the intracellular levels of these proteins can be regulated by techniques available in the art. For example, p46 or p48 levels can be increased by infecting cells with a retroviral or an adenoviral vector which expresses the desired protein at higher levels necessary for suppression of mutations in the Rb gene or in other oncogenic or tumor suppressor genes. Alternatively, levels of these proteins can be reduced in the cells by inserting antisense oiigonucleotides to suppress expression of the protein products in the cell . Oiigonucleotides may be inserted into specific cells by methods known in the art, such as by polycationic carriers or by encapsulation in lipid vectors.

While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the composition, methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

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SEQUENCE LISTING

(1) GENERAL INFORMATION:

(i) APPLICANT:

NAME: BOARD OF REGENTS, THE UNIVERSITY OF TEXAS SYSTEM STREET: 201 West 7th Street CITY: Austin

STATE: Texas

COUNTRY: United States of America POSTAL CODE: 78701 TELEPHONE NO: (512)499-4462 TELEFAX: (512)499-4523

(ii) INVENTORS: QIAN, Yue-Wei

LEE, Eva Y.-H. P.

(iii) TITLE OF INVENTION: NOVEL PROTEINS WHICH BIND

TO RETINOBLASTOMA PROTEINS AND THEIR ENCODING DNA SEQUENCES

(iv) NUMBER OF SEQUENCES: 10

(v) CORRESPONDENCE ADDRESS:

(A) ADDRESSEE: Arnold, White & Durkee

(B) STREET: P.O. Box 4433 (C) CITY: Houston

(D) STATE: Texas

(E) COUNTRY: USA

(F) ZIP: 77210

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(A) MEDIUM TYPE: Floppy disk

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(D) SOFTWARE: Patentin Release #1.0, Version

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(vii) CURRENT APPLICATION DATA:

(A) APPLICATION NUMBER: Unknown

(B) FILING DATE: Concurrently herewith

(C) CLASSIFICATION: Unknown

(viii) PRIOR APPLICATION DATA:

(A) APPLICATION NUMBER: USSN 08/105,454

(B) FILING DATE: 12 AUGUST 1993 (12.08.93)

(C) CLASSIFICATION: UNKNOWN

(ix) ATTORNEY/AGENT INFORMATION:

(A) NAME: KITCHELL, BARBARA S.

(B) REGISTRATION NUMBER: 33,928

(C) REFERENCE/DOCKET NUMBER: UTFK196P--

(x) TELECOMMUNICATION INFORMATION:

(A) TELEPHONE: 512/320-7200

(B) TELEFAX: 713/789-2679

(C) TELEX: 79-0924

(2) INFORMATION FOR SEQ ID NO:1 :

(i) SEQUENCE CHARACTERISTICS:

(A) LENGTH: 2314 base pairs (B) TYPE: nucleic acid

(C) STRANDEDNESS: single

(D) TOPOLOGY: linear

(ii) MOLECULE TYPE: DNA (genomic)

(ix) FEATURE:

(A) NAME/KEY: CDS (B) LOCATION: 85..1362

(xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:

5

CGCGCGCACA GAGCGAGCTC TTGCAGCCTC CCCGCCCCTC CCGCAACGCT CGACCCCAGG 60

ATTCCCCCGG CTCGCCTGCC CGCCATGGCC GACAAGGAAG CAGCCTTCGA CGACGCAGTG 120

10 GAAGAACGAG TGATCAACGA GGAATACAAA ATATGGAAAA AGAACACCCC TTTTCTTTAT 180

GATTTGGTGA TGACCCATGC TCTGGAGTGG CCCAGCCTAA CTGCCCAGTG GCTTCCAGAT 240

GTAACCAGAC CAGAAGGGAA AGATTTCAGC ATTCATCGAC TTGTCCTGGG GACACACACA 300

15 TCGGATGAAC AAAACCATCT TGTTATAGCC AGTGTGCAGC TCCCTAATGA TGATGCTCAG 360

TTTGATGCGT CACACTACGA CAGTGAGAAA GGAGAATTTG GAGGTTTTGG TTCAGTTAGT 420

20 GGAAAAATTG AAATAGAAAT CAAGATCAAC CATGAAGGAG AAGTAAACAG GGCCCGTTAT 480

ATGCCCCAGA ACCCTTGTAT CATCGCAACA AAGACTCCTT CCAGTGATGT TCTTGTCTTT 540

GACTATACAA AACATCCTTC TAAACCAGAT CCTTCTGGAG AGTGCAACCC AGACTTGCGT 600

CTCCGTGGAC ATCAGAAGGA AGGCTATGGG CTTTCTTGGA ACCCAAATCT CAGTGGGCAC 660

5 TTACTTAGTG CTTCAGATGA CCATACCATC TGCCTGTGGG ACATCAGTGC CGTTCCAAAG 720

GAGGGAAAAG TGGTAGATGC GAAGACCATC TTTACAGGGC ATACGGCAGT AGTAGAAGAT 780

GTTTCCTGGC ATCTACTCCA TGAGTCTCTG TTTGGGTCAG TTGCTGATGA TCAGAAACTT 840 10

ATGATTTGGG ATACTCGTTC AAACAATACT TCCAAACCAA GCCACTCAGT TGATGCTCAC 900

ACTGCTGAAG TGAACTGCCT TTCTTTCAAT CCTTATAGTG AGTTCATTCT TGCCACAGGA 960

15 TCAGCTGACA AGACTGTTGC CTTGTGGGAT CTGAGAAATC TGAAACTTAA GTTGCATTCC 1020

TTTGAGTCAC ATAAGGATGA AATATTCCAG GTTCAGTGGT CACCTCACAA TGAGACTATT 1080

TTAGCTTCCA GTGGTACTGA TCGCAGACTG AATGTCTGGG ATTTAAGTAA AATTGGAGAG 1140

GAACAATCCC CAGAAGATGC AGAAGACGGG CCACCAGAGT TGTTGTTTAT TCATGGTGGT 1200

CATACTGCCA AGATATCTGA TTTCTCCTGG AATCCCAATG AACCTTGGGT GATTTGTTCT 1260

GTATCAGAAG ACAATATCAT GCAAGTGTGG CAAATGGCAG AGAACATTTA TAATGATGAA 1320

GACCCTGAAG GAAGCGTGGA TCCAGAAGGA CAAGGGTCCT AGATATGTCT TTACTTGTTG 1380

5 TGATTTTAGA CTCCCCTTTT TTCTTCTCAA CCCTGAGAGT GATTTAACAC TGGTTTTGAG 1440

ACAGACTTTA TTCAGCTATC CCTCTATATA ATAGGTACCA CCGATAATGC TATTAGCCCA 1500

AACCGTGGGT TTTTCTAAAT ATTAATAGGG GGGCTTGATT CAACAAAGCC ACAGACTTAA 1560

10 CGTTGAAATT TTCTTCAGGA ATTTTCTAGT AACCCAGGTC TAAAGTAGCT ACAGAAAGGG 1620

GAATATTATG TGTGATTATT TTTCTTCTTA TGCTATATCC CCAAGTTTTT CAGACTCATT 1680

15 TAAGTAAAGG CTAGAGTGAG TAAGGAATAG AGCCAAATGA GGTAGGTGTC TGAGCCATGA 1740

AGTATAAATA CTGAAAGATG TCACTTTTAT TCAGGAAATA GGGGGAGTTC AAGTCGTATA 1800

GATTCCTACT CGAAAATCTT GACACCTGAC TTTCCAGGAT GCACATTTTC ATACGTAGAC 1860

20

CAGTTTCCTC TTGGTTTCTT CAGTTAAGTC AAAACAACAC GTTCCTCTTT CCCCATATAT 1920

TCATATATTT TTGCTCGTTA GTGTATTTCT TGAGCTGTTT TCATGTTGTT TATTTCCTGT 1980

CTGTGAAATG GTGTTTTTTT TTTTGTTGTT GGTTTTTTTT TTTTTTTTTT AACTTGGGAC 2040

CACCAAGTTG TAAAGATGTA TGTTTTTACC TGACAGTTAT ACCACAGGTA GACTGTCAAG 2100

5 TTGAGAAGAG TGAATCAATA ACTTGTATTT GTTTTAAAAA TTAAATTAAT CCTTGATAAG 2160

AGTTGCTTTT TTTTTTTAGG AGTTAGTCCT TGACCACTAG TTTGATGCCA TCTCCATTTT 2220

GGGTGACCTG TTTCACCAGC AGGCCTGTTA CTCTCCATGA CTAACTGTGT AAGTGCTTAA 2280

10 AATGGAATAA ATTGCTTTTC TACATAAAAA AAAA 2314

(2) INFORMATION FOR SEQ ID NO:2 :

15

(i) SEQUENCE CHARACTERISTICS:

(A) LENGTH: 425 amino acids

(B) TYPE: amino acid (D) TOPOLOGY: linear

20

(ii) MOLECULE TYPE: protein

(xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:

Met Ala Asp Lys Glu Ala Ala Phe Asp Asp Ala Val Glu Glu Arg Val

1 5 10 15

He Asn Glu Glu Tyr Lys He Trp Lys Lys Asn Thr Pro Phe Leu Tyr 5 20 25 30

Asp Leu Val Met Thr His Ala Leu Glu Trp Pro Ser Leu Thr Ala Gin 35 40 45

10 Trp Leu Pro Asp Val Thr Arg Pro Glu Gly Lys Asp Phe Ser He His 50 55 60

Arg Leu Val Leu Gly Thr His Thr Ser Asp Glu Gin Asn His Leu Val 65 70 75 80

15

He Ala Ser Val Gin Leu Pro Asn Asp Asp Ala Gin Phe Asp Ala Ser

85 90 95

His Tyr Asp Ser Glu Lys Gly Glu Phe Gly Gly Phe Gly Ser Val Ser 20 100 105 110

Gly Lys He Glu He Glu He Lys He Asn His Glu Gly Glu Val Asn

115 120 125

Arg Ala Arg Tyr Met Pro Gin Asn Pro Cys He He Ala Thr Lys Thr

Pro Ser Ser Asp Val Leu Val Phe Asp Tyr Thr Lys His Pro Ser Lys 5 145 150 155 160

Pro Asp Pro Ser Gly Glu Cys Asn Pro Asp Leu Arg Leu Arg Gly His

165 170 175

10 Gin Lys Glu Gly Tyr Gly Leu Ser Trp Asn Pro Asn Leu Ser Gly His

180 185 190

Leu Leu Ser Ala Ser Asp Asp His Thr He Cys Leu Trp Asp He Ser 195 200 205

15

Ala Val Pro Lys Glu Gly Lys Val Val Asp Ala Lys Thr He Phe Thr 210 215 220

Gly His Thr Ala Val Val Glu Asp Val Ser Trp His Leu Leu His Glu 20 225 230 235 240

Ser Leu Phe Gly Ser Val Ala Asp Asp Gin Lys Leu Met He Trp Asp

245 250 255

Thr Arg Ser Asn Asn Thr Ser Lys Pro Ser His Ser Val Asp Ala His

Thr Ala Glu Val Asn Cys Leu Ser Phe Asn Pro Tyr Ser Glu Phe He

5 275 280 285

Leu Ala Thr Gly Ser Ala Asp Lys Thr Val Ala Leu Trp Asp Leu Arg 290 295 300

10 Asn Leu Lys Leu Lys Leu His Ser Phe Glu Ser His Lys Asp Glu He 305 310 315 320

Phe Gin Val Gin Trp Ser Pro His Asn Glu Thr He Leu Ala Ser Ser

325 330 335

15

Gly Thr Asp Arg Arg Leu Asn Val Trp Asp Leu Ser Lys He Gly Glu 340 345 350

Glu Gin Ser Pro Glu Asp Ala Glu Asp Gly Pro Pro Glu Leu Leu Phe 20 355 360 365

He His Gly Gly His Thr Ala Lys He Ser Asp Phe Ser Trp Asn Pro 370 375 380

Asn Glu Pro Trp Val He Cys Ser Val Ser Glu Asp Asn He Met Gin

Val Trp Gin Met Ala Glu Asn He Tyr Asn Asp Glu Asp Pro Glu Gly 5 405 410 415

Ser Val Asp Pro Glu Gly Gin Gly Ser 420 425

10

(2) INFORMATION FOR SEQ ID NO:3 :

(i) SEQUENCE CHARACTERISTICS: <

(A) LENGTH: 18 amino acids

15 (B) TYPE: amino acid

(C) STRANDEDNESS: single

(D) TOPOLOGY: linear

(ii) MOLECULE TYPE: protein

20

(xi) SEQUENCE DESCRIPTION: SEQ ID NO:3

Glu Asn Leu Phe Cys Ser Glu Glu Met Pro Ser Ser Asp Asp Glu Ala

1 5 10 15

Ala Thr 5

(2) INFORMATION FOR SEQ ID NO:4 :

(i) SEQUENCE CHARACTERISTICS: 10 (A) LENGTH: 18 amino acids

(B) TYPE: amino acid

(C) STRANDEDNESS: single

(D) TOPOLOGY: linear

15 (ii) MOLECULE TYPE: protein

(xi) SEQUENCE DESCRIPTION: SEQ ID NO:4 :

Glu Asn Leu Phe Cys Ser Lys Glu Met Pro Ser Ser Asp Asp Glu Ala

( 2 ) INFORMATION FOR SEQ ID NO : 5 :

(i) SEQUENCE CHARACTERISTICS:

(A) LENGTH: 5 amino acids

(B) TYPE: amino acid

(C) STRANDEDNESS: single

(D) TOPOLOGY: linear

(ii) MOLECULE TYPE: protein

10

(xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:

I c

Glu Gly Gin Gly Ser o

I 1 5

15

(2) INFORMATION FOR SEQ ID NO: 6:

(i) SEQUENCE CHARACTERISTICS: 20 (A) LENGTH: 18 amino acids

(D) TOPOLOGY: linear

(ii) MOLECULE TYPE: protein

(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 6:

5 Ala Ala Asn Lys Ala Arg Lys Glu Ala Glu Leu Ala Ala Ala Asn Ala 1 5 10 15

Glu Gin

10

(2) INFORMATION FOR SEQ ID NO:7:

(i) SEQUENCE CHARACTERISTICS:

(A) LENGTH: 20 base pairs

15 (B) TYPE: nucleic acid

(C) STRANDEDNESS: single

(D) TOPOLOGY: linear

(A) NAME/KEY: R

(B) LOCATION: 3, 15, and 18

(C) IDENTIFICATION METHOD: R = A or G

(ix) FEATURE:

(A) NAME/KEY: Y (B) LOCATION: 6

(C) IDENTIFICATION METHOD: Y = C or T

(ix) FEATURE:

(A) NAME/KEY: H (B) LOCATION: 9

(C) IDENTIFICATION METHOD: H = A or C or T

(ix) FEATURE:

(A) NAME/KEY: B (B) LOCATION: 12

(C) IDENTIFICATION METHOD: B = G or T or C

(ix) FEATURE:

(A) NAME/KEY: M (B) LOCATION: 19

(C) IDENTIFICATION METHOD: M = A or C

(xi) SEQUENCE DESCRIPTION: SEQ ID NO:7 :

GARGAYACHG TBGARGARMG 20

(2) INFORMATION FOR SEQ ID NO: 8:

(i) SEQUENCE CHARACTERISTICS:

(A) LENGTH: 23 base pairs

(B) TYPE: nucleic acid

(C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA

(ix) FEATURE:

(A) NAME/KEY: R 5 (B) LOCATION: 3, 15 and 21

(C) IDENTIFICATION METHOD: R = A or G

(ix) FEATURE:

(A) NAME/KEY: Y 10 (B) LOCATION: 6, 9 and 18

(C) IDENTIFICATION METHOD: Y = C or T

(xi) SEQUENCE DESCRIPTION: SEQ ID NO:8 :

15 GTRTTYTTYT TCCARATYTT RTA 23

(2) INFORMATION FOR SEQ ID NO: 9 :

20 (i) SEQUENCE CHARACTERISTICS:

(A) LENGTH: 1929 base pairs

(B) TYPE: nucleic acid

(C) STRANDEDNESS: single

(D) TOPOLOGY : linear

(ii) MOLECULE TYPE: DNA

(xi) SEQUENCE DESCRIPTION: SEQ ID NO:9 :

GGAGGCGCGG GTTGAAAAGT CTCGTTCCAA GTTTGGAGAG AGAGAGAAGA GCGCCTCAGA 60

CCTCGGTACC CGCGAGCGGG GAGGACCCAG GAAAGAAGGA CGCGGCGTCT GGGGAGCACC 120

10

CAGGCAGCAA GACGGGGCCC GGGCTTTCGA CAGTGGGGAG TGTGACGCGC TTGGGAAAGG 180 c

CAGGAGCGCC AGCGGTCGGG CTGCTCTTGG CTAACGAGAG GAGTCCGAGG CGGCGGCGAG 240

15 GGGCGAACGA CCCGACGCAA GATGGCGAGT AAAGAGATGT TTGAAGATAC TGTGGAGGAG 300

CGTGTCATCA ATGAAGAATA TAAAATCTGG AAGAAGAATA CACCGTTTCT ATATGACCTG 360

GTTATGACCC ATGCTCTTCA GTGGCCCAGT CTTACCGTTC AGTGGCTTCC TGAAGTGACT 420

20

AAACCTGAAG GAAAAGATTA TGCCCTTCAT TGGCTAGTGC TGGGGACTCA TACGTCTGAT 480

GAGCAGAATC ATCTGGTGGT TGCTCGAGTA CATATTCCCA ATGATGATGC ACAGTTTGAT 540

GCTTCCCATT GTGACAGTGA CAAGGGTGAA TTTGGTGGCT TTGGTTCTGT AACAGGAAAA 600

ATTGAATGTG AAATTAAAAT CAATCACGAA GGAGAAGTAA ACCGTGCTCG TTACATGCCG 660

5 CAGAATCCTC ACATCATTGC TACAAAAACA CCATCTTCTG ATGTGTTGGT TTTTGACTAT 720

ACAAAACACC CTGCTAAACC AGACCCAAGT GGAGAATGTA ATCCTGATCT CAGATTAAGA 780

GGTCACCAGA AGGAAGGCTA TGGTCTCTCC TGGAATTCAA ATTTGAGTGG ACATCTCCTA 840 10

AGTGCATCTG ATGACCATAC TGTTTGTCTG TGGGATATAA ACGCAGGACC AAAAGAAGGC 900 I c

AAAATTGTGG ATGCTAAAGC CATCTTTACT GGCCACTCAG CTGTTGTAGA GGATGTGGCC 960

15 TGGCACCTGC TGCACGAGTC ATTGTTTGGA TCTGTTGCTG ATGATCAGAA ACTTATGATA 1020

TGGGACACCA GGTCCAATAC CACCTCCAAG CCGAGTCACT TGGTGGATGC GCACACTGCC 1080

GAAGTCAACT GCCTCTCATT CAATCCCTAC AGCGAATTTA TTCTAGCCAC CGGCTCTGCG 1140

20

GATAAGACCG TAGCTTTATG GGATCTGCGT AACTTAAAAT TAAAACTCCA TACCTTCGAA 1200

TCTCATAAAG ATGAAATTTT CCAGGTCCAC TGGTCTCCAC ATAATGAAAC TATTCTGGCT 1260

TCAAGTGGTA CTGACCGCCG CCTGAATGTG TGGGATTTAA GTAAAATTGG GGAAGAACAA 1320

TCAGCAGAAG ATGCAGAAGA TGGGCCTCCA GAACTCCTGT TTATTCATGG AGGACACACT 1380

5 GCTAAGATTT CAGATTTTAG CTGGAACCCC AATGAGCCTT GGGTCATTTG CTCAGTGTCT 1440

GAGGATAACA TCATGCAGAT ATGGCAAATG GCTGAAAATA TTTACAATGA TGAAGAGTCA 1500

GATGTCACGA CATCCGAACT GGAGGGACAA GGATCTTAAA CCCAAAGTAC GAGAAATGTT 1560

10

TCTGTTGAAT GTAATGCTAC ATGAATGCTT GATTTATCAA GCGCCAAAAA GGCATTGTAT 1620

AGTAGGAAAT GTAAGTGGGG TGGCTTATGG CTTCTTTATC CTCTGATTCT AGCACTTTCA 1680

15 AGTGAGCTGT TGCGTACTGT ATCATATTGT AGCTATTAGG GAAGAGAAGA ATGTTGCTTA 1740

AGAAAGAACA TCACCATTGA TTTTAAATAC AACTAGCAGG GTATTGCCTT TGATTCAACT 1800

GTTTTAAGTC CTCATTTTCT CAAACTAAGT GCTTGCTGTT CCCAAATATG CAAGAATAAC 1860

20

TTTTACACTT TTTCCTTCCA ACACTTCTTG ATTGGCTTTG CAGAAATAAA GTTTTAAAAT 1920

AAAAAAAAA 1929

(2) INFORMATION FOR SEQ ID NO:10:

(i) SEQUENCE CHARACTERISTICS: 5 (A) LENGTH: 425 amino acid residues

(B) TYPE: amino acid

(C) STRANDEDNESS: single

(D) TOPOLOGY: linear

10 (ii) MOLECULE TYPE: protein

(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 10:

15 Met Ala Ser Lys Glu Met Phe Glu Asp Thr Val Glu Glu Arg Val He 1 5 10 15

Asn Glu Glu Tyr Lys He Trp Lys Lys Asn Thr Pro Phe Leu Tyr Asp 20 25 30

20

Leu Val Met Thr His Ala Leu Gin Trp Pro Ser Leu Thr Val Gin Trp

Leu Pro Glu Val Thr Lys Pro Glu Gin Lys Asp Tyr Ala Leu His Trp

Leu Val Leu Gly Thr His Thr Ser Asp Glu Gin Asn His Leu Val Val 5 65 70 75 80

Ala Arg Val His He Pro Asn Asp Asp Ala Gin Phe Asp Ala Ser His

85 90 95

10 Cys Asp Ser Asp Lys Gly Glu Phe Gly Gly Phe Gly Ser Val Thr Gly

100 105 110 I c

Lys He Glu Cys Glu He Lys He Asn His Glu Gly Glu Val Asn Arg 115 120 125

15

Ala Arg Tyr Met Pro Gin Asn Pro His He He Ala Thr Lys Thr Pro 130 135 140

Ser Ser Asp Val Leu Val Phe Asp Tyr Thr Lys His Pro Ala Lys Pro

Asp Pro Ser Gly Glu Cys Asn Pro Asp Leu Arg Leu Arg Gly His Gin

165 170 175

Lys Glu Gly Tyr Gly Leu Ser Trp Asn Ser Asn Leu Ser Gly His Leu

Leu Ser Ala Ser Asp Asp His Thr Val Cys Leu Trp Asp He Asn Ala 5 195 200 205

Gin Pro Lys Glu Gly Lys He Val Asp Ala Lys Ala He Phe Thr Gly 210 215 220

10 His Ser Ala Val Val Glu Asp Val Ala Trp His Leu Leu His Glu Ser 225 230 235 240 I

Leu Phe Gly Ser Val Ala Asp Asp Gin Lys Leu Met He Trp Asp Thr

245 250 255

15

Arg Ser Asn Thr Thr Ser Lys Pro Ser His Leu Val Asp Ala His Thr 260 265 270

Ala Glu Val Asn Cys Leu Ser Phe Asn Pro Tyr Ser Glu Phe He Leu 20 275 280 285

Ala Thr Gly Ser Ala Asp Lys Thr Val Ala Leu Trp Asp Leu Arg Asn

290 295 300

Leu Lys Leu Lys Leu His Thr Phe Glu Ser His L s As Glu He Phe

Gin Val His Trp Ser Pro His Asn Glu Thr He Leu Ala Ser Ser Gly 5 325 330 335

Thr Asp Arg Arg Leu Asn Val Trp Asp Leu Ser Lys He Gly Glu Glu 340 345 350

10 Gin Ser Ala Glu Asp Ala Glu Asp Gly Pro Pro Glu Leu Leu Phe He 355 360 365 I 0

I

His Gly Gly His Thr Ala Lys He Ser Asp Phe Ser Trp Asn Pro Asn 370 375 380

15

Glu Pro Trp Val He Cys Ser Val Ser Glu Asp Asn He Met Gin He 385 390 395 400

Trp Gin Met Ala Glu Asn He Tyr Asn Asp Glu Glu Ser Asp Val Thr

Thr Ser Glu Leu Glu Gly Gin Gly Ser 420 425

Claims

CLAIMS :

1. A DNA segment comprising an isolated gene encoding a protein or polypeptide having an amino acid sequence in accordance with the amino acid sequence set forth in SEQ ID NO:2 or the amino acid sequence set forth in SEQ ID NO:10.

2. The DNA segment of claim 1, wherein said DNA segment encodes a p48 protein or polypeptide comprising an amino acid sequence in accordance with the amino acid sequence set forth in SEQ ID NO:2.

3. The DNA segment of claim 2, wherein said DNA segment includes a nucleic acid sequence in accordance with the nucleic acid sequence set forth in SEQ ID N0:1.

4. The DNA segment of claim 3, wherein said DNA segment has the nucleic sequence of SEQ ID N0:1.

5. The DNA segment of claim 1, wherein said DNA segment encodes a p46 protein or polypeptide comprising an amino acid sequence in accordance with the amino acid sequence set forth in SEQ ID NO:10.

6. The DNA segment of claim 5, wherein said DNA segment includes a nucleic acid sequence in accordance with the nucleic acid sequence set forth in SEQ ID NO:9.

7. The DNA segment of claim 6, wherein said DNA segment has the nucleic acid sequence of SEQ ID NO:9.

8. The DNA segment of claim 1, wherein said DNA segment is positioned under the control of a promoter.

9. The DNA segment of claim 8, wherein said DNA segment is positioned under the control of a recombinant promoter.

10. The DNA segment of claim 1 further defined as a recombinant vector.

11. The DNA segment of claim 10, wherein said vector is a recombinant expression vector capable of expressing a p48 protein or polypeptide on introduction into a host cell.

12. The DNA segment of claim 11, wherein said vector comprises a nucleic acid sequence in accordance with SEQ ID N0:1.

13. The recombinant vector of claim 10, wherein said vector is a recombinant expression vector capable of expressing a p46 protein or polypeptide on introduction into a host cell.

14. The recombinant expression vector of claim 13, wherein said vector comprises a nucleic acid sequence in accordance with SEQ ID NO: 9.

15. The recombinant expression vector of claim 10, wherein said vector is a multicopy plasmid.

16. The recombinant expression vector of claim 10, wherein said vector is capable of being transformed into and expressed in a yeast host cell .

17. The recombinant expression of claim 16, wherein said vector is derived from plasmid YEpl3.

18. A recombinant host cell comprising a DNA segment in accordance with claim 1.

19. The recombinant host cell of claim 18, wherein said host cell is a procaryotic cell.

20. The recombinant host cell of claim 18, wherein said cell is a eucaryotic cell.

21. The recombinant host cell of claim 20, wherein said cell is a yeast cell.

22. The recombinant host cell of claim 18, wherein said DNA segment is introduced into the cell by means of a recombinant vector.

23. The recombinant host cell of claim 22, wherein said recombinant vector is an expression vector and said host cell expresses a recombinant p48 protein or polypeptide.

24. The recombinant host cell of claim 23, wherein said expression vector comprises a nucleic acid sequence in accordance with the nucleic acid sequence of SEQ ID N0:1.

25. The recombinant host cell of claim 22, wherein said recombinant vector is an expression vector and said host cell expresses a recombinant p46 protein or polypeptide.

26. The recombinant host cell of claim 25, wherein said expression vector comprises a nucleic acid sequence in accordance with the nucleic acid sequence of SEQ ID NO:9.

27. A nucleic acid segment which comprises at least a 10 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID N0:1 or SEQ ID NO:9.

28. The nucleic acid segment of claim 27, further defined as comprising at least a 15 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID N0:1 or SEQ ID NO:9.

29. The nucleic acid segment of clam 28, further defined as comprising at least a 20 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID N0:1 or SEQ ID NO:9.

30. The nucleic acid segment of claim 29, further defined as comprising at least a 30 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID NO:l or SEQ ID NO:9.

31. The nucleic acid segment of claim 30, further defined as comprising at least a 50 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID NO:l or SEQ ID NO:9.

32. The nucleic acid segment of claim 31, further defined as comprising at least a 100 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID NO:l or SEQ ID NO:9.

33. The nucleic acid segment of claim 32, further defined as comprising at least a 1000 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID NO:l or SEQ ID NO:9.

34. The nucleic acid segment of claim 33, further defined as comprising at least a 2291 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID NO:l.

35. The nucleic acid segment of claim 34, further defined as having the nucleic acid sequence of SEQ ID N0:1.

36. The nucleic acid segment of claim 33, further defined as comprising at least a 1668 nucleotide long stretch which corresponds to the nucleic acid sequence of SEQ ID NO:9.

37. The nucleic acid segment of claim 36, further defined as having the nucleic acid sequence of SEQ ID NO:9.

38. The nucleic acid of claim 27, further defined as comprising a nucleic acid fragment of up to 10,000 basepairs in length.

39. The nucleic acids segment of claim 38, further defined as comprising a nucleic acid fragment of up to 5,000 basepairs in length.

40. The nucleic acid segment of claim 39, further defined as comprising a nucleic acid fragment of up to 3,000 basepairs in length.

41. The nucleic acid segment of claim 40, further defined as comprising a nucleic acid fragment of up to 1,000 basepairs in length.

42. The nucleic acid segment of claim 41, further defined as comprising a nucleic acid fragment of up to 500 basepairs in length.

43. The nucleic acid segment of claim 42, further defined as comprising a nucleic acid fragment of up to 100 basepairs in length.

44. The nucleic acid segment of claim 43, further defined as comprising a nucleic acid fragment of up to 50 basepairs in length.

45. The nucleic acid segment of claim 27, further defined as a DNA segment.

46. A method of using a DNA segment encoding a p48 or p46 protein or polypeptide, comprising the steps of:

preparing a recombinant vector in which said DNA segment is positioned under the control of a promoter;

introducing said recombinant vector into a host cell;

culturing said host cell under conditions effective to allow expression of the encoded p48 or p46 protein or polypeptide; and

collecting said expressed p48 or p46 protein or polypeptide.

47. The method of claim 46, wherein said DNA segment encodes a p48 protein or polypeptide.

48. The method of claim 46, wherein said DNA segment encodes a p46 protein or polypeptide.

49. The method of claim 46, wherein said recombinant vector is a plasmid.

50. The method of claim 46, wherein said host cell is a yeast cell.

51. A method of producing a recombinant p48 or p46 protein or polypeptide, comprising culturing yeast cells capable of expressing recombinant p48 or p46 under conditions effective to obtain a p48 or p46 protein or polypeptide.

52. The method of claim 51, wherein said yeast cells are capable of expressing a recombinant p48 protein or polypeptide.

53. The method of claim 51, wherein said yeast cells are capable of expressing a recombinant p46 protein or polypeptide.

54. A composition, free from total cellular components, comprising a p48 or p46 protein or polypeptide capable of interacting with retinoblastoma protein (Rb) , wherein the protein or polypeptide includes an amino acid sequence in accordance with the amino acid sequence set forth in SEQ ID NO:2 or SEQ ID NO:10.

55. The composition of claim 54, comprising a p48 protein having an amino acid sequence as set forth in SEQ ID NO:2.

56. The composition of claim 54, comprising a p46 protein having an amino acid sequence as set forth in SEQ ID NO:10.

57. The composition of claim 54, preparable by subjecting an extract from mammalian cells to fractionation and collecting a fraction containing the p48 or p46 protein or polypeptide.

58. The composition of claim 54, preparable by the steps of:

obtaining an extract from mammalian cells;

subjecting said extract to fractionation by affinity chromatography using a retinoblastoma protein (Rb) affinity column;

identifying a positive fraction containing a p48 or p46 protein or polypeptide capable of interacting with the retinoblastoma protein (Rb) ; and

collecting said positive fraction.

59. The composition of claim 54, wherein the p48 or p46 protein or polypeptide is a substantially purified protein or polypeptide.

60. The composition of claim 54, wherein the p48 or p46 protein or polypeptide is a recombinant protein or polypeptide.

61. The composition of claim 60, wherein said recombinant p48 or p46 protein or polypeptide is preparable by subjecting an extract from recombinant p48- expressing or recombinant p46-expressing yeast cells to fractionation and collecting a fraction containing the p48 or p46 protein or polypeptide.

62. A substantially purified p48 protein or polypeptide,

63. A substantially purified p46 protein or polypeptide,

64. An antibody having binding affinity for a p48 or p46 protein or polypeptide which comprises an amino acid sequence in accordance with the amino acid sequence set forth in SEQ ID NO:2 or SEQ ID NO:10.

65. The antibody of claim 64, wherein the antibody is a polyclonal antibody.

66. The antibody of claim 64, wherein the antibody is a monoclonal antibody.