CARK PROTEIN AND NUCLEIC ACID MOLECULES AND USES THEREFOR

Abstract: The invention provides isolated nucleic acids molecules, designated CARK nucleic acid molecules. The invention also provides antisense nucleic acid molecules, recombinant expression vectors containing CARK nucleic acid molecules, host cells into which the expression vectors have been introduced, and nonhuman transgenic animals in which a CARK gene has been introduced or disrupted. The invention still further provides isolated CARK proteins, fusion proteins, antigenic peptides and anti-CARK antibodies. Diagnostic methods utilizing compositions of the invention are also provided.

Description: CARK PROTEIN NUCLEIC ACID MOLECULES AND USES THEREFOR Background of the Invention Phosphate tightly associated with protein has been known since the late nineteenth century. Since then, a variety of covalent linkages of phosphate to proteins have been found. The most common involve esterification of phosphate to serine, threonine, and tyrosine with smaller amounts being linked to lysine, arginine, histidine, aspartic acid, glutamic acid, and cysteine. The occurrence of phosphorylated proteins implies the existence of one or more protein kinases capable of phosphorylating amino acid residues on proteins, and also of protein phosphatases capable of hydrolyzing phosphorylated amino acid residues on proteins. Protein kinases play critical roles in the regulation of biochemical and morphological changes associated with cellular growth and division (D'Urso, G. et al. (1990) Science 250: 786-791 ; Birchmeier. C. et al. (1993) Bioessays 15: 185-189). They serve as growth factor receptors and signal transducers and have been implicated in cellular transformation and malignancy (Hunter, T. et al. (1992) Cell 70: 375-387; Posada, J. et al. (1992) Mol. Biol. Cell 3: 583-592; Hunter, T. et al. (1994) Cell 79: 573- 582). For example, protein kinases have been shown to participate in the transmission of signals from growth-factor receptors (Sturgill, T. W. et al. (1988) Nature 344: 715- 718; Gomez, N. et al. (1991) Nature 353: 170-173), control of entry of cells into mitosis (Nurse, P. (1990) Nature 344: 503-508; Mailer, J. L. (1991) Curr. Opin. Cell Biol. 3: 269-275) and regulation of actin bundling (Husain-Chishti, A. et al. (1988) Nature 334: 718-721). Protein kinases can be divided into two main groups based on either amino acid sequence similarity or specificity for either serine/threonine or tyrosine residues. A small number of dual-specificity kinases are structurally like the serine/threonine - specific group. Within the broad classification, kinases can be further sub-divided into families whose members share a higher degree of catalytic domain amino acid sequence identity and also have similar biochemical properties. Most protein kinase family members also share structural features outside the kinase domain that reflect their particular cellular roles. These include regulatory domains that control kinase activity or interaction with other proteins (Hanks, S.K. et al. (1988) Science 241 : 42-52). For example, kinases which contain ankyrin repeat domains have been identified, such as the Integrin-linked kinase (ILK). ILK is an ankyrin repeat containing serine-threonine protein kinase which interacts with integrin β t and β 3 heterodimeric transmembrane glycoprotein subunit cytoplasmic domains. Integrins communicate with cell surface and cytoplasmic molecules such as cytoskeletal and catalytic signaling proteins (Hannigan G.E. et al. (1981) Nature 379:91-96, Schwartz M.A. et al. (1995) Annu. Rev. Cell Dev. Biol. 1 1 :549-599). Overexpression of ILK increases the expression of cyclin A, cyclin D ] and Cdk4 proteins by overriding the adhesion-dependent regulation of cell cycle progression through G ] into S phase. This activity suggests that ILK may be an important regulator of integrin-mediated cell cycle progression (Radeva G. et al. (1997) J. Biol. Chem. 272:13937-13944). Overexpression of ILK also stimulates fibronectin matrix assembly in epithelial cells (Wu C. et al. (1998) J. Biol. Chem. 273:528-536). Summary of the Invention The present invention is based, at least in part, on the discovery of novel ankyrin repeat containing kinases. referred herein as "Cardiac-related Ankyrin-Repeat Protein Kinase" ("CARK") nucleic acid and protein molecules. The CARK molecules of the present invention are useful as modulating agents for regulating a variety of cellular processes, e.g.. cardiac cellular processes. Accordingly, in one aspect, this invention provides isolated nucleic acid molecules encoding CARK proteins or biologically active portions thereof, as well as nucleic acid fragments suitable as primers or hybridization probes for the detection of CARK-encoding nucleic acids. In one embodiment, a CARK nucleic acid molecule of the invention is at least 50%. 55%, 60%. 65%. 70%, 75%, 80%, 85%, 90%, 95%, 98%, or more identical to the nucleotide sequence (e.g.. to the entire length of the nucleotide sequence) shown in SEQ ID ΝOJ or 3 or the nucleotide sequence of the DΝA insert of the plasmid deposited with ATCC as Accession Number , or a complement thereof. In one embodiment, a CARK nucleic acid molecule ofthe invention is at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 82%, 85%, 90%, 95%, 98%, or more identical to the nucleotide sequence (e.g., to the entire length ofthe nucleotide sequence) shown in SEQ ID NO:7 or 9 or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number , or a complement thereof. In a preferred embodiment, the isolated nucleic acid molecule includes the nucleotide sequence shown SEQ ID NOJ or 3, or a complement thereof. In another embodiment, the nucleic acid molecule includes SEQ ID NOJ and nucleotides 1-47 of SEQ ID NOJ . In another embodiment, the nucleic acid molecule includes SEQ ID NOJ and nucleotides 2553-3025 of SEQ ID NOJ . In another preferred embodiment, the nucleic acid molecule consists of the nucleotide sequence shown in SEQ ID NOJ or 3. In another preferred embodiment, the nucleic acid molecule includes a fragment of at least 467 nucleotides (e.g., 467 contiguous nucleotides) of the nucleotide sequence of SEQ ID NO: lor 3, or a complement thereof. In a preferred embodiment, the isolated nucleic acid molecule includes the nucleotide sequence shown SEQ ID NO: 7 or 9, or a complement thereof. In another embodiment, the nucleic acid molecule includes SEQ ID NO:9 and nucleotides 1-60 of SEQ ID NO:7. In another embodiment, the nucleic acid molecule includes SEQ ID NO:9 and nucleotides 2566-3026 of SEQ ID NO:7. In another preferred embodiment, the nucleic acid molecule consists of the nucleotide sequence shown in SEQ ID NO: 7 or 9. In another preferred embodiment, the nucleic acid molecule includes a fragment of at least 2962 nucleotides (e.g., 2962 contiguous nucleotides) of the nucleotide sequence of SEQ ID NO:7or 9, or a complement thereof. In another embodiment, a CARK nucleic acid molecule includes a nucleotide sequence encoding a protein having an amino acid sequence sufficiently homologous to the amino acid sequence of SEQ ID NO:2 or 8, or an amino acid sequence encoded by the DNA insert of the plasmid deposited with ATCC as Accession Number . In a preferred embodiment, a CARK nucleic acid molecule includes a nucleotide sequence encoding a protein having an amino acid sequence at least 50%), 55%, 60%>, 65%>, 70%, 75%). 80%), 85%, 90%, 95%, 98% or more homologous to the entire length ofthe amino acid sequence of SEQ ID NO:2, or the amino acid sequence encoded by the DNA insert of the plasmid deposited with ATCC as Accession Number . In another preferred embodiment, a CARK nucleic acid molecule includes a nucleotide sequence encoding a protein having an amino acid sequence at least 50%, 55%, 60%, 65%), 10%, 75%, 80%, 85%, 90%. 92%, 95%, 98% or more homologous to the entire length ofthe amino acid sequence of SEQ ID NO: 8, or the amino acid sequence encoded by the DNA insert ofthe plasmid deposited with ATCC as Accession Number . In another preferred embodiment, an isolated nucleic acid molecule encodes the amino acid sequence of human CARK. In yet another preferred embodiment, the nucleic acid molecule includes a nucleotide sequence encoding a protein having the amino acid sequence of SEQ ID NO:2, or the amino acid sequence encoded by the DNA insert ofthe plasmid deposited with ATCC as Accession Number . In yet another preferred embodiment, the nucleic acid molecule is at least 467 nucleotides in length. In a further preferred embodiment, the nucleic acid molecule is at least 467 nucleotides in length and encodes a protein having a CARK activity (as described herein). In another preferred embodiment, an isolated nucleic acid molecule encodes the amino acid sequence of rat CARK. In yet another preferred embodiment, the nucleic acid molecule includes a nucleotide sequence encoding a protein having the amino acid sequence of SEQ ID NO:8. or the amino acid sequence encoded by the DNA insert of the plasmid deposited with ATCC as Accession Number . In yet another preferred embodiment, the nucleic acid molecule is at least 2962 nucleotides in length. In a further preferred embodiment, the nucleic acid molecule is at least 2962 nucleotides in length and encodes a protein having a CARK activity (as described herein). Another embodiment ofthe invention features nucleic acid molecules, preferably CARK nucleic acid molecules, which specifically detect CARK nucleic acid molecules relative to nucleic acid molecules encoding non-CARK proteins. For example, in one embodiment, such a nucleic acid molecule is at least 250-300, 300-350, 350-400, 400- 450, 467, 467-500, 500-550. or 550-600, 600-800, 800-1000, 1000-1200, 1200-1400, 1400-1600, 1600-1800. 1800-2000, 2000-2400, 2400-2800, 2800-2900, 2962, or more nucleotides in length and hybridizes under stringent conditions to a nucleic acid molecule comprising the nucleotide sequence shown in SEQ ID NOJ, 3, 7, or 9, or, the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number , or a complement thereof. In preferred embodiments, the nucleic acid molecules are at least 15 (e.g., contiguous) nucleotides in length and hybridize under stringent conditions to nucleotides 1-47, 94-294, 318-338, 1 145-1364, 1833-1921 , 2051-2267, 2290-2543, or 3018-3025 of SEQ ID NO: 1. In other preferred embodiments, the nucleic acid molecules comprise nucleotides 1-47. 94-294, 318-338, 1 145-1364, 1833-1921 , 2051-2267, 2290-2543, or 3018-3025 of SEQ ID NOJ . In other preferred embodiments, the nucleic acid molecules consist of nucleotides 1-47, 94-294, 318-338, 1 145-1364, 1833-1921, 2051- 2267, 2290-2543. or 3018-3025 of SEQ ID NOJ . In other preferred embodiments, the nucleic acid molecule encodes a naturally occurring allelic variant of a polypeptide comprising the amino acid sequence of SEQ ID NO:2 or 8, or an amino acid sequence encoded by the DNA insert ofthe plasmid deposited with ATCC as Accession Number , wherein the nucleic acid molecule hybridizes to a nucleic acid molecule comprising SEQ ID NOJ or 3, or SEQ ID NO:7 or 9, respectively, under stringent conditions. Another embodiment ofthe invention provides an isolated nucleic acid molecule which is antisense to a CARK nucleic acid molecule, e.g., the coding strand of a CARK nucleic acid molecule. Another aspect of the invention provides a vector comprising a CARK nucleic acid molecule. In certain embodiments, the vector is a recombinant expression vector. In another embodiment, the invention provides a host cell containing a vector of the invention. In yet another embodiment, the invention provides a host cell containing a nucleic acid molecule ofthe invention. The invention also provides a method for producing a protein, preferably a CARK protein, by culturing in a suitable medium, a host cell, e.g.. a mammalian host cell such as a non-human mammalian cell, ofthe invention containing a recombinant expression vector, such that the protein is produced. Another aspect of this invention features isolated or recombinant CARK proteins and polypeptides. In one embodiment, the isolated protein, preferably a CARK protein, includes at least one ankyrin repeat domain, and preferably two, three, four, five, six, seven, eight, or. most preferably, nine or more ankyrin repeat domains. In another embodiment, the isolated protein, preferably a CARK protein, includes at least one protein kinase domain. In a preferred embodiment, the protein, preferably a CARK protein, includes at least one ankyrin repeat domain and preferably two. three, four, five, six, seven, eight, or, most preferably, nine or more ankyrin repeat domains, and has an amino acid sequence at least about 50%, 55%, 60%, 65%, 70%, 75%. 80%, 85%, 90%, 92%o, 95%o, 98%) or more homologous to the amino acid sequence of SEQ ID NO:2 or 8. or the amino acid sequence encoded by the DNA insert ofthe plasmid deposited with ATCC as Accession Number . In another preferred embodiment, the protein, preferably a CARK protein, includes at least one protein kinase domain and has an amino acid sequence at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%. 85%, 90%, 92%o. 95%o, 98%o or more homologous to the amino acid sequence of SEQ ID NO:2 or 8, or the amino acid sequence encoded by the DNA insert of the plasmid deposited with ATCC as Accession Number . In yet another preferred embodiment, the protein, preferably a CARK protein, includes at least one ankyrin repeat domain and preferably two, three, four, five, six, seven, eight, or, most preferably, nine or more ankyrin repeat domains, at least one protein kinase domain, and has an amino acid sequence at least about 50%, 55%. 60%, 65%, 70%, 75%, 80%, 85%, 90%, 92%, 95%. 98% or more homologous to the amino acid sequence of SEQ ID NO:2 or 8, or the amino acid sequence encoded by the DNA insert ofthe plasmid deposited with ATCC as Accession Number . In another preferred embodiment, the protein, preferably a CARK protein, includes at least one ankyrin repeat domain and preferably two, three, four, five, six. seven, eight, or, most preferably, nine or more ankyrin repeat domains and has a CARK activity, as described herein. In yet another preferred embodiment, the protein, preferably a CARK protein, includes a protein kinase domain and has a CARK activity. as described herein. In a further preferred embodiment, the protein, preferably a CARK protein, includes at least one ankyrin repeat domain and preferably two, three, four. five. six, seven, eight, or, most preferably, nine or more ankyrin repeat domains, at least one protein kinase domain, and has a CARK activity, as described herein. In yet another preferred embodiment, the protein, preferably a CARK protein, includes at least one ankyrin repeat domain and preferably two, three, four, five, six, seven, eight, or, most preferably, nine or more ankyrin repeat domains and is encoded by a nucleic acid molecule having a nucleotide sequence which hybridizes under stringent hybridization conditions to a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO: 1 , 3, 7, or 9. In a further embodiment, the protein, preferably a CARK protein, includes at least one protein kinase domain and is encoded by a nucleic acid molecule having a nucleotide sequence which hybridizes under stringent hybridization conditions to a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NOJ, 3, 7, or 9. In another preferred embodiment, the protein, preferably a CARK protein, includes at least one ankyrin repeat domain and preferably two, three, four, five, six, seven, eight, or, most preferably, nine or more ankyrin repeat domains, at least one protein kinase domain, and is encoded by a nucleic acid molecule having a nucleotide sequence which hybridizes under stringent hybridization conditions to a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NOJ, 3, 7, or 9. In another embodiment, the invention features fragments of the protein having the amino acid sequence of SEQ ID NO:2 or 8, wherein the fragment comprises at least 15 amino acids (e.g., contiguous amino acids) ofthe amino acid sequence of SEQ ID NO:2 or 8 or an amino acid sequence encoded by the DNA insert of the plasmid deposited with the ATCC as Accession Number . In another embodiment, the protein, preferably a CARK protein, has the amino acid sequence of SEQ ID NO:2 or 8. In another embodiment, the invention features an isolated protein, preferably a CARK protein, which is encoded by a nucleic acid molecule consisting of a nucleotide sequence at least about 50%, 55%, 60%, 65%, 70%. 75%, 80%, 82%, 85%. 90%. 95%, 98%> or more homologous to a nucleotide sequence of SEQ ID NOJ, 3, 7. or 9, or a complement thereof. This invention further features an isolated protein, preferably a CARK protein, which is encoded by a nucleic acid molecule consisting of a nucleotide sequence which hybridizes under stringent hybridization conditions to a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NOJ , 3, 7, or 9. or a complement thereof. The proteins of the present invention or portions thereof, e.g., biologically active portions thereof, can be operatively linked to a non-CARK polypeptide (e.g., heterologous amino acid sequences) to form fusion proteins. The invention further features antibodies, such as monoclonal or polyclonal antibodies, that specifically bind proteins ofthe invention, preferably CARK proteins. In addition, the CARK proteins or biologically active portions thereof can be incoφorated into pharmaceutical compositions, which optionally include pharmaceutically acceptable carriers. In another aspect, the present invention provides a method for detecting the presence of a CARK nucleic acid molecule, protein or polypeptide in a biological sample by contacting the biological sample with an agent capable of detecting a CARK nucleic acid molecule, protein or polypeptide such that the presence of a CARK nucleic acid molecule, protein or polypeptide is detected in the biological sample. In another aspect, the present invention provides a method for detecting the presence of CARK activity in a biological sample by contacting the biological sample with an agent capable of detecting an indicator of CARK activity such that the presence of CARK activity is detected in the biological sample. In another aspect, the invention provides a method for modulating CARK activity comprising contacting a cell capable of expressing CARK with an agent that modulates CARK activity such that CARK activity in the cell is modulated. In one embodiment, the agent inhibits CARK activity. In another embodiment, the agent stimulates CARK activity. In one embodiment, the agent is an antibody that specifically binds to a CARK protein. In another embodiment, the agent modulates expression of CARK by modulating transcription of a CARK gene or translation of a CARK mRNA. In yet another embodiment, the agent is a nucleic acid molecule having a nucleotide sequence that is antisense to the coding strand of a CARK mRNA or a CARK gene. In one embodiment, the methods of the present invention are used to treat a subject having a disorder characterized by aberrant or unwanted CARK protein or nucleic acid expression or activity by administering an agent which is a CARK modulator to the subject. In one embodiment, the CARK modulator is a CARK protein. In another embodiment the CARK modulator is a CARK nucleic acid molecule. In yet another embodiment, the CARK modulator is a peptide, peptidomimetic. or other small molecule. In a preferred embodiment, the disorder characterized by aberrant or unwanted CARK protein or nucleic acid expression is a cardiovascular disorder. The present invention also provides a diagnostic assay for identifying the presence or absence of a genetic alteration characterized by at least one of (i) aberrant modification or mutation of a gene encoding a CARK protein; (ii) mis-regulation of the gene; and (iii) aberrant post-translational modification of a CARK protein, wherein a wild-type form of the gene encodes a protein with a CARK activity. In another aspect the invention provides a method for identifying a compound that binds to or modulates the activity of a CARK protein, by providing an indicator composition comprising a CARK protein having CARK activity, contacting the indicator composition with a test compound, and determining the effect ofthe test compound on CARK activity in the indicator composition to identify a compound that modulates the activity of a CARK protein. Other features and advantages of the invention will be apparent from the following detailed description and claims. Brief Description of the Drawings Figure 1 depicts the cDNA sequence and predicted amino acid sequence of human CARK. The nucleotide sequence corresponds to nucleic acids 1 to 3025 of SEQ ID NO: 1. The amino acid sequence corresponds to amino acids 1 to 835 of SEQ ID NO: 2. The coding region without the 5' and 3' untranslated regions ofthe human CARK gene is shown in SEQ ID NOJ. Figure 2 depicts a structural, hydrophobicity, and antigenicity analysis ofthe human CARK protein. Figure 3 depicts an alignment of the CARK protein with the A. Thaliana kinase 2 (Accession No.Z97337), A. Thaliana kinase 3 (Accession No. AC0031 13), Arabidopsis thaliana (Accession No. AL031 135), C. elegans kinase (Accession No. AF024491). D. discoideum protein tyrosine kinase (Accession No. A35670), D. discoideum protein tyrosine kinase (Accession No. U01064), H. sapiens serine/threonine kinase (Accession No. Z48615), human rafl (Accession No. W13107). human Rafl kinase (Accession No. R98215), and soybean kinase (Accession No. M67449) using the Clustal method with a PAM250 residue weight table. Figure 4 depicts the results of a search which was performed against the HMM database in which ankyrin repeat domains and a protein kinase domain were identified in the human CARK protein. Figure 5 depicts the cDNA sequence and predicted amino acid sequence of rat CARK. The nucleotide sequence corresponds to nucleic acids 1 to 3026 of SEQ ID NO:7. The amino acid sequence corresponds to amino acids 1 to 835 of SEQ ID NO: 8. The coding region without the 5' and 3' untranslated regions ofthe rat CARK gene is shown in SEQ ID NO:9. Figure 6 depicts the results of a search which was performed against the HMM database in which ankyrin repeat domains and a protein kinase domain were identified in the rat CARK protein. Figure 7 depicts a global alignment of the human CARK nucleic acid sequence with the rat CARK nucleic acid sequence using the GAP program in the GCG software package, using a nwsgapdna matrix a gap weight of 12 and a length weight of 4. The results showed a 82.2% identity between the two sequences. Figure 8 depicts a global alignment ofthe human CARK protein with the rat CARK protein using the GAP program in the GCG software package, using a Blosum 62 matrix and a gap weight of 12 and a length weight of 4. The results showed a 91.4% identity between the two sequences. Detailed Description of the Invention The present invention is based, at least in part, on the discover}' of novel molecules, referred to herein as "Cardiac -related Ankyrin-Repeat Protein Kinase" or "CARK" nucleic acid and protein molecules, which play a role in or function in signaling pathways associated with cellular growth or differentiation. In one embodiment, the CARK molecules modulate the activity of one or more proteins involved in cellular growth or differentiation, e.g.. cardiac cell growth or differentiation. In another embodiment, the CARK molecules ofthe present invention are capable of modulating the phosphorylation state of a CARK molecule or one or more proteins involved in cellular growth or differentiation, e.g., cardiac cell growth or differentiation. In a preferred embodiment, the CARK molecules are protein kinases, e.g., serine/threonine protein kinases, which are expressed and/or function in cells ofthe cardiovascular system, e.g., cells ofthe heart, the blood vessels, and/or the blood. As used herein, the term "protein kinase" includes a protein or polypeptide which is capable of modulating its own phosphorylation state or the phosphorylation state of another protein or polypeptide. Protein kinases (described in, for example. Hanks S.K. et al. (1995) FASEB J.9:576-596) can have a specificity for (i.e.. a specificity to phosphorylate) serine/threonine residues, tyrosine residues, or both serine/threonine and tyrosine residues, e.g., the dual specificity kinases. There are a number of conserved regions in the catalytic domain of protein kinases. One of these regions, located in the N-terminal extremity ofthe catalytic domain, is a glycine-rich stretch of residues in the vicinity of a lysine residue, which is believed to be involved in ATP binding. Another region, located in the central part ofthe catalytic domain, contains a conserved aspartic acid residue which is important for the catalytic activity ofthe enzyme (Knighton D.R. et al. (1991) Science 253:407-414). Two signature patterns have been described for this region: one specific for serine/ threonine kinases and one for tyrosine kinases. Protein kinase polypeptides ofthe present invention preferably include one ofthe following consensus sequences: [LIV] -G-{P}-G-{P}- [FY MGSTNH] - [SGA] -{PW}- [LIVCAT] -{PD}~x [GSTACLIVMFY] -x(5,18) - [LIVMFY CSTAR] - [AIVP] - [LIVMFAGCKR] -K (SEQ ID NO: 4) [K binds ATP] [LIV FYC] -X- [HY] -x-D- [LIVMFY] -K-x(2) -N- [LIVMFYCT] (3) (SEQ ID NO: 5) [D is an active site residue] [LIVMFYC] -x- [HY] -x-D- [LIVMFY] - [RSTAC] -x(2) -N- [LIVMFYC] (3; (SEQ ID NO: 6) [D is an active site residue] The signature patterns or consensus patterns described herein are described according to the following designation: all amino acids are indicated according to their universal single letter designations: "x" designates any amino acid; x (n) designates n number of amino acids, e.g., x(2) designates any 2 amino acids, e.g., x(l-3) designates any of one to three amino acids; and. amino acids in brackets indicates any one ofthe amino acids within the brackets, e.g.. [HY] indicates any one of either H (histidine) or Y (tyrosine). Protein kinases play a role in signaling pathways associated with cellular growth and differentiation. For example, protein kinases are involved in the regulation of signal transmission from cellular receptors, e.g., growth-factor receptors; entry of cells into mitosis; and the regulation of cytoskeleton function, e.g., actin bundling. Thus, the CARK molecules of the present invention may be involved in: 1) the regulation of transmission of signals from cellular receptors, e.g., cardiac cell growth factor receptors; 2) the modulation ofthe entry of cells, e.g., cardiac precursor cells, into mitosis; 3) the modulation of cellular differentiation; 4) the modulation of cell death; and 5) the regulation of cytoskeleton function, e.g., actin bundling. Inhibition or over stimulation ofthe activity of protein kinases involved in signaling pathways associated with cellular growth can lead to perturbed cellular growth, which can in turn lead to cellular growth related disorders. As used herein, a "cellular growth related disorder" includes a disorder, disease, or condition characterized by a deregulation, e.g.. an upregulation or a downregulation, of cellular growth. Cellular growth deregulation may be due to a deregulation of cellular proliferation, cell cycle progression, cellular differentiation and/or cellular hypertrophy. Examples of cellular growth related disorders include cardiovascular disorders such as heart failure, congenital heart disease, cardiac myocyte hypertrophy, hypertension, atrial fibrillation, dilated cardiomyopathy. idiopathic cardiomyopathy. or angina; and proliferative disorders and/or differentiative disorders such as cancer, e.g., melanoma, prostate cancer, cervical cancer, breast cancer, colon cancer, leukemia, carcinoma, or sarcoma. As used herein, the term "cardiovascular disorder" includes a disease, disorder, or state involving the cardiovascular system, e.g., the heart, the blood vessels, and/or the blood. A cardiovascular disorder can be caused by an imbalance in arterial pressure, a malfunction of the heart, or an occlusion of a blood vessel, e.g., by a thrombus. Examples of such disorders include congenital heart defects (e.g., atrioventricular canal defects), hypertension, atherosclerosis, coronary artery spasm, coronary artery disease, valvular disease, ischemia reperfusion injury, restenosis, arterial inflammation, vascular wall remodeling, ventricular remodeling, rapid ventricular pacing, coronary microembolism, tachycardia, bradycardia, pressure overload, aortic bending, coronary artery ligation, vascular heart disease, long-QT syndrome, congestive heart failure, sinus node dysfunction, atrial flutter, myocardial infarction, coronary artery spasm, arrhythmias, and cardiomyopathies. As used herein, the term "congestive heart failure" includes a condition characterized by a diminished capacity of the heart to supply the oxygen demands of the body. Symptoms and signs of congestive heart failure include diminished blood flow to the various tissues ofthe body, accumulation of excess blood in the various organs, e.g., when the heart is unable to pump out the blood returned to it by the great veins, exertional dyspnea, fatigue, and/or peripheral edema, e.g., peripheral edema resulting from left ventricular dysfunction. Congestive heart failure may be acute or chronic. The manifestation of congestive heart failure usually occurs secondary to a variety of cardiac or systemic disorders that share a temporal or permanent loss of cardiac function. Examples of such disorders include hypertension, coronary artery disease, valvular disease, and cardiomyopathies, e.g., hypertrophic, dilative, or restrictive cardiomyopathies. Congestive heart failure is described in, for example, Cohn J.N. et al. (1998) American Family Physician 57: 1901-04, the contents of which are incoφorated herein by reference. CARK-associated or related disorders include disorders associated with the atrioventricular canal defects (AVCD) locus on human chromosome 1 , e.g., congenital heart defects (Sheffield. VC et al. (1997) Human Molecular Genetics, 6: 1 17-121 ). CARK-associated or related disorders also include disorders of tissues in which CARK is expressed, e.g.. heart and skeletal muscle. The present invention is based, at least in part, on the discovery of novel molecules, referred to herein as CARK protein and nucleic acid molecules, which comprise a family of molecules having certain conserved structural and functional features. The term "family" when referring to the protein and nucleic acid molecules of the invention is intended to mean two or more proteins or nucleic acid molecules having a common structural domain or motif and having sufficient amino acid or nucleotide sequence homology as defined herein. Such family members can be naturally or non- naturally occurring and can be from either the same or different species. For example, a family can contain a first protein of human origin, as well as other, distinct proteins of human origin or alternatively, can contain homologues of non-human origin. Members of a family may also have common functional characteristics. For example, the family of CARK proteins comprise at least one, and preferably two, three, four, five, six, seven, eight, or most preferably, nine or more ankyrin repeat domains. As used herein, the term "ankyrin repeat domain" includes a protein domain involved in proteimprotein interactions, having an amino acid sequence of about 20-40 amino acid residues and having a bit score for the alignment ofthe sequence to the ankyrin repeat domain (HMM) of at least 1. Preferably, an ankyrin repeat domain includes at least about 25-40, more preferably about 25-35 amino acid residues, or most preferably about 30-35 amino acids and has a bit score for the alignment of the sequence to the ankyrin repeat domain (HMM) of at least 3, 5, 10, 20, 30, 40, 50, or greater. The ankyrin repeat domain (HMM) has been assigned the PFAM Accession PF00023 (http://genome.wustl.edu/Pfam/.html). Ankyrin repeats are described in, for example. Otto E. et al. (1991) J. Biol. Chem. 114:241-253, Hatada E.N. et al. (1992) RNJS USA 89:2489-2493, and Blank V.P. et al. (1992) Trends Genet. 8:144-149, the contents of which are incorporated herein by reference. To identify the presence of an ankyrin repeat domain in a CARK protein, and make the determination that a protein of interest has a particular profile, the amino acid sequence ofthe protein is searched against a database of HMMs (e.g., the Pfam database, release 2J) using the default parameters (http://www.sanger.ac.uk Software/Pfam/HMM_search). For example, the hmmsf program, which is available as part ofthe HMMER package of search programs, is a family specific default program for MILPAT0063 and a score of 15 is the default threshold score for determining a hit. Alternatively, the threshold score for determining a hit can be lowered (e.g., to 8 bits). A description of the Pfam database can be found in Sonhammer et al. (1997) Proteins 28(3)405-420 and a detailed description of HMMs can be found, for example, in Gribskov et α/.(1990) Meth. Enzymol. 183: 146-159; Gribskov et α/.(1987) Proc. Natl. Acad. Sci. USA 84:4355-4358; Krogh et α/.(1994) J. Mol. Biol. 235: 1501-1531 ; and Stultz et α/.( 1993) Rrσtem Scz. 2:305-314, the contents of which are incoφorated herein by reference. A search was performed against the HMM database resulting in the identification of nine ankyrin repeat domains in the amino acid sequence of human CARK (SEQ ID NO:2) at about residues 66-99. 100-132, 133-165, 168-198, 199-233, 234-268, 269-302, 306-338, and 339-371 of SEQ ID NO:2. The results ofthe search are set forth in Figure 4. Nine ankyrin repeat domains were also identified in the amino acid sequence of rat CARK (SEQ ID NO:8) at about residues 66- 99, 100-132, 133-165, 168-198, 199-233, 234-264, 269-302, 306-338, and 339-371 of SEQ ID NO:8. The results ofthe search are set forth in Figure 6. In a further preferred embodiment, an ankyrin repeat domain includes at least about 25-40, more preferably about 25-35 amino acid residues, or about 30-35 amino acids and has at least 50-60%) homology, preferably about 60-70%>. more preferably about 70-80%), or about 80-90%) homology with an ankyrin repeat domain of human or rat CARK (e.g., residues 66-99, 100-132, 133-165, 168-198. 199-233, 234-268, 269- 302, 306-338, and 339-371 of SEQ ID NO:2; or residues 66-99, 100-132, 133-165, 168- 198, 199-233, 234-264, 269-302, 306-338, and 339-371 of SEQ ID NO:8 ). In another embodiment, a CARK of the present invention is identified based on the presence of a "protein kinase domain" in the protein or corresponding nucleic acid molecule. As used herein, the term " protein kinase domain " includes a protein domain having an amino acid sequence of about 200-400 amino acid residues and having a bit score for the alignment of the sequence to the protein kinase domain (HMM) of at least 200. Preferably, a protein kinase domain includes at least about 200-300, and more preferably about 250-300 amino acid residues, and has a bit score for the alignment of the sequence to the protein kinase domain (HMM) of at least 210. 220, 230. 250, 300 or greater. The protein kinase domain (HMM) has been assigned the PFAM Accession PF00069 (http://genome.wustl.edu/Pfam/.html). To identify the presence of a protein kinase domain in a CARK protein, and make the determination that a protein of interest has a particular profile, the amino acid sequence of the protein is searched against a database of HMMs as described above. A search was performed against the HMM database resulting in the identification of a protein kinase domain in the amino acid sequence of human CARK (SEQ ID NO:2) at about residues 463-716 of SEQ ID NO:2. The results ofthe search are set forth in Figure 4. A protein kinase domain was also identified in the amino acid sequence of rat CARK (SEQ ID NO:8) at about residues 463-716 of SEQ ID NO:8. The results ofthe search are set forth in Figure 6. In another preferred embodiment, a protein kinase domain includes at least about 200-400, more preferably about 200-300 amino acid residues, or about 250-300 amino acids and has at least 50-60%> homology, preferably about 60-70%>, more preferably about 70-80%), or about 80-90%) homology with a protein kinase domain of human or rat CARK (e.g., residues 463-716 of SEQ ID NO:2 or 8). Accordingly. CARK proteins having at least 50-60%) homology, preferably about 60-70%), more preferably about 70-80%), or about 80-90%) homology with an ankyrin repeat domain or a protein kinase domain of human or rat CARK are within the scope of the invention. Isolated proteins ofthe present invention, preferably CARK proteins, have an amino acid sequence sufficiently homologous to the amino acid sequence of SEQ ID NO:2 or 8 or are encoded by a nucleotide sequence sufficiently homologous to SEQ ID NOJ , 3, 7, or 9. As used herein, the term "sufficiently homologous" refers to a first amino acid or nucleotide sequence which contains a sufficient or minimum number of identical or equivalent (e.g.. an amino acid residue which has a similar side chain) amino acid residues or nucleotides to a second amino acid or nucleotide sequence such that the first and second amino acid or nucleotide sequences share common structural domains or motifs and/or a common functional activity. For example, amino acid or nucleotide sequences which share common structural domains have at least 30%o. 40%>, or 50%) homology, preferably 60%) homology, more preferably 70%>-80%>, and even more preferably 90-95%) homology across the amino acid sequences of the domains and contain at least one and preferably two structural domains or motifs, are defined herein as sufficiently homologous. Furthermore, amino acid or nucleotide sequences which share at least 30%), 40%), or 50%o, preferably 60%), more preferably 70-80%, or 90-95%) homology and share a common functional activity are defined herein as sufficiently homologous. As used interchangeably herein, a "CARK activity", "biological activity of CARK" or "functional activity of CARK", refers to an activity exerted by a CARK protein, polypeptide or nucleic acid molecule on a CARK responsive cell or on a CARK protein substrate, as determined in vivo, or in vitro, according to standard techniques. In one embodiment, a CARK activity is a direct activity, such as an association with a CARK-target molecule. As used herein, a "target molecule" or "binding partner" is a molecule with which a CARK protein binds or interacts in nature, such that CARK- mediated function is achieved. A CARK target molecule can be a non-CARK molecule or a CARK protein or polypeptide ofthe present invention. In an exemplary embodiment, a CARK target molecule is a CARK ligand. Alternatively, a CARK activity is an indirect activity, such as a cellular signaling activity mediated by interaction of the CARK protein with a CARK ligand. The biological activity of CARK is described herein. Accordingly, another embodiment ofthe invention features isolated CARK proteins and polypeptides having a CARK activity. Preferred proteins are CARK proteins having at least one ankyrin repeat domain and preferably two, three, four, five, six. seven, eight, or, most preferably, nine or more ankyrin repeat domains, and, preferably, a CARK activity. Other preferred proteins are CARK proteins having a protein kinase domain and, preferably, a CARK activity. Yet other preferred proteins have at least one ankyrin repeat domain and preferably two, three, four, five, six, seven, eight, or, most preferably, nine or more ankyrin repeat domains, a protein kinase domain, and. preferably, a CARK activity. Additional preferred proteins have at least one ankyrin repeat domain and preferably two, three, four, five, six, seven, eight, or. most preferably, nine or more ankyrin repeat domains, a protein kinase domain, and are. preferably, encoded by a nucleic acid molecule having a nucleotide sequence which hybridizes under stringent hybridization conditions to a nucleic acid molecule comprising the nucleotide sequence of SEQ ID NOJ , 3, 7. or 9. The nucleotide sequence of the isolated human CARK cDNA and the predicted amino acid sequence of the human CARK polypeptide are shown in Figure 1 and in SEQ ID NOsJ and 2, respectively. A plasmid containing the nucleotide sequence encoding human CARK was deposited with the American Type Culture Collection (ATCC), 10801 University Boulevard, Manassas, VA 201 10-2209, on and assigned Accession Number . This deposit will be maintained under the terms of the Budapest Treaty on the International Recognition ofthe Deposit of Microorganisms for the Puφoses of Patent Procedure. This deposit was made merely as a convenience for those of skill in the art and is not an admission that a deposit is required under 35 U.S.C. §112. The human CARK gene, which is approximately 3025 nucleotides in length, encodes a protein having a molecular weight of approximately 96 kD and which is approximately 835 amino acid residues in length. The nucleotide sequence ofthe isolated rat CARK cDNA and the predicted amino acid sequence of the rat CARK polypeptide are shown in Figure 5 and in SEQ ID NOs:7 and 8, respectively. A plasmid containing the nucleotide sequence encoding rat CARK was deposited with the American Type Culture Collection (ATCC), 10801 University Boulevard, Manassas, VA 201 10-2209. on and assigned Accession Number . This deposit will be maintained under the terms of the Budapest Treaty on the International Recognition ofthe Deposit of Microorganisms for the Puφoses of Patent Procedure. This deposit was made merely as a convenience for those of skill in the art and is not an admission that a deposit is required under 35 U.S.C. §1 12. The rat CARK gene, which is approximately 3026 nucleotides in length, encodes a protein having a molecular weight of approximately 96 kD and which is approximately 835 amino acid residues in length. Various aspects ofthe invention are described in further detail in the following subsections: I. Isolated Nucleic Acid Molecules One aspect of the invention pertains to isolated nucleic acid molecules that encode CARK proteins or biologically active portions thereof, as well as nucleic acid fragments sufficient for use as hybridization probes to identify CARK-encoding nucleic acid molecules (e.g., CARK mRNA) and fragments for use as PCR primers for the amplification or mutation of CARK nucleic acid molecules. As used herein, the term "nucleic acid molecule" is intended to include DNA molecules (e.g., cDNA or genomic DNA) and RNA molecules (e.g., mRNA) and analogs of the DNA or RNA generated using nucleotide analogs. The nucleic acid molecule can be single-stranded or double- stranded, but preferably is double-stranded DNA. The term "isolated nucleic acid molecule" includes nucleic acid molecules which are separated from other nucleic acid molecules which are present in the natural source ofthe nucleic acid. For example, with regards to genomic DNA. the term "isolated" includes nucleic acid molecules which are separated from the chromosome with which the genomic DNA is naturally associated. Preferably, an "isolated" nucleic acid is free of sequences which naturally flank the nucleic acid (i.e., sequences located at the 5' and 3' ends of the nucleic acid) in the genomic DNA of the organism from which the nucleic acid is derived. For example, in various embodiments, the isolated CARK nucleic acid molecule can contain less than about 5 kb, 4kb, 3kb. 2kb, 1 kb, 0.5 kb or 0J kb of nucleotide sequences which naturally flank the nucleic acid molecule in genomic DNA ofthe cell from which the nucleic acid is derived. Moreover, an "isolated" nucleic acid molecule, such as a cDNA molecule, can be substantially free of other cellular material, or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. A nucleic acid molecule ofthe present invention, e.g., a nucleic acid molecule having the nucleotide sequence of SEQ ID NOJ, 3. 7, or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number , or a portion thereof, can be isolated using standard molecular biology techniques and the sequence information provided herein. Using all or portion ofthe nucleic acid sequence of SEQ ID NOJ, 3, 7. or 9, or the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number . as a hybridization probe. CARK nucleic acid molecules can be isolated using standard hybridization and cloning techniques (e.g.. as described in Sambrook, J.. Fritsh, E. F., and Maniatis, T. Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, Cold Spring Harbor. NY, 1989). Moreover, a nucleic acid molecule encompassing all or a portion of SEQ ID NOJ, 3, 7, or 9. or the nucleotide sequence ofthe DNA insert ofthe plasmid deposited with ATCC as Accession Number can be isolated by the polymerase chain reaction (PCR) using synthetic oligonucleotide primers designed based upon the sequence of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number . A nucleic acid of the invention can be amplified using cDNA, mRNA or alternatively, genomic DNA, as a template and appropriate oligonucleotide primers according to standard PCR amplification techniques. The nucleic acid so amplified can be cloned into an appropriate vector and characterized by DNA sequence analysis. Furthermore, oligonucleotides corresponding to CARK nucleotide sequences can be prepared by standard synthetic techniques, e.g., using an automated DNA synthesizer. In a preferred embodiment, an isolated nucleic acid molecule of the invention comprises the nucleotide sequence shown in SEQ ID NO: 1. The sequence of SEQ ID NOJ corresponds to the human CARK cDNA. This cDNA comprises sequences encoding the human CARK protein (i.e., "the coding region", from nucleotides 48- 2552), as well as 5' untranslated sequences (nucleotides 1 -47) and 3' untranslated sequences (nucleotides 2553-3025). Alternatively, the nucleic acid molecule can comprise only the coding region of SEQ ID NOJ (e.g., nucleotides 48-2552, corresponding to SEQ ID NOJ). In another preferred embodiment, an isolated nucleic acid molecule ofthe invention comprises the nucleotide sequence shown in SEQ ID NO:7. The sequence of SEQ ID NO: 7 corresponds to the rat CARK cDNA. This cDNA comprises sequences encoding the rat CARK protein (i.e., "the coding region", from nucleotides 61-2565), as well as 5' untranslated sequences (nucleotides 1-60) and 3' untranslated sequences (nucleotides 2566-3026). Alternatively, the nucleic acid molecule can comprise only the coding region of SEQ ID NO:7 (e.g., nucleotides 61-2565, corresponding to SEQ ID NO:9). In another preferred embodiment, an isolated nucleic acid molecule of the invention comprises a nucleic acid molecule which is a complement of the nucleotide sequence shown in SEQ ID NOJ , 3, 7, or 9, or the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number , or a portion of any of these nucleotide sequences. A nucleic acid molecule which is complementary to the nucleotide sequence shown in SEQ ID NOJ, 3, 7, or 9 or the nucleotide sequence of the DNA insert ofthe plasmid deposited with ATCC as Accession Number . is one which is sufficiently complementary to the nucleotide sequence shown in SEQ ID NOJ. 3. 7, or 9. or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number , such that it can hybridize to the nucleotide sequence shown in SEQ ID NOJ , 3, 7, or 9, or the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number , thereby forming a stable duplex. In still another preferred embodiment, an isolated nucleic acid molecule ofthe present invention comprises a nucleotide sequence which is at least about 50%, 55%o. 60%, 65%, 70%. 75%, 80%, 82%, 85%, 90%, 95%, 98% or more homologous to the entire length ofthe nucleotide sequence shown in SEQ ID NOJ, 3, 7. or 9, or the entire length ofthe nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number , or a portion of any of these nucleotide sequences. Moreover, the nucleic acid molecule of the invention can comprise only a portion ofthe nucleic acid sequence of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number , for example, a fragment which can be used as a probe or primer or a fragment encoding a portion of a CARK protein, e.g., a biologically active portion of a CARK protein. The nucleotide sequence determined from the cloning ofthe CARK gene allows for the generation of probes and primers designed for use in identifying and/or cloning other CARK family members, as well as CARK homologues from other species. The probe/primer typically comprises substantially purified oligonucleotide. The oligonucleotide typically comprises a region of nucleotide sequence that hybridizes under stringent conditions to at least about 12 or 15, preferably about 20 or 25, more preferably about 30, 35, 40, 45, 50, 55, 60, 65, or 75 consecutive nucleotides of a sense sequence of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number , of an anti-sense sequence of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number , or of a naturally occurring allelic variant or mutant of SEQ ID NO: 1 , 3, 7, or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number . In an exemplary embodiment, a nucleic acid molecule ofthe present invention comprises a nucleotide sequence which is greater than 250-300, 300-350, 350-400, 400- 450, 467, 467-500, 500-550, or 550-600, 600-800, 800-1000. 1000-1200, 1200-1400, 1400-1600, 1600-1800, 1800-2000, 2000-2400, 2400-2800, 2800-2900, 2962 or more nucleotides in length and hybridizes under stringent hybridization conditions to a nucleic acid molecule of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number . Probes based on the CARK nucleotide sequences can be used to detect transcripts or genomic sequences encoding the same or homologous proteins. In preferred embodiments, the probe further comprises a label group attached thereto, e.g., the label group can be a radioisotope, a fluorescent compound, an enzyme, or an enzyme co-factor. Such probes can be used as a part of a diagnostic test kit for identifying cells or tissue which misexpress a CARK protein, such as by measuring a level of a CARK- encoding nucleic acid in a sample of cells from a subject e.g., detecting CARK mRNA levels or determining whether a genomic CARK gene has been mutated or deleted. A nucleic acid fragment encoding a "biologically active portion of a CARK protein" can be prepared by isolating a portion of the nucleotide sequence of SEQ ID NOJ , 3, 7, or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number , which encodes a polypeptide having a CARK biological activity (the biological activities of the CARK proteins are described herein), expressing the encoded portion ofthe CARK protein (e.g., by recombinant expression in vitro) and assessing the activity of the encoded portion of the CARK protein. The invention further encompasses nucleic acid molecules that differ from the nucleotide sequence shown in SEQ ID NOJ , 3. 7. or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number , due to degeneracy of the genetic code and thus encode the same CARK proteins as those encoded by the nucleotide sequence shown in SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number . In another embodiment, an isolated nucleic acid molecule of the invention has a nucleotide sequence encoding a protein having an amino acid sequence shown in SEQ ID NO:2 or 8. In addition to the CARK nucleotide sequences shown in SEQ ID NO: 1 , 3, 7, or 9. or the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number . it will be appreciated by those skilled in the art that DNA sequence polymoφhisms that lead to changes in the amino acid sequences of the CARK proteins may exist within a population (e.g., the human population). Such genetic polymoφhism in the CARK genes may exist among individuals within a population due to natural allelic variation. As used herein, the terms "gene" and "recombinant gene" refer to nucleic acid molecules which include an open reading frame encoding a CARK protein, preferably a mammalian CARK protein, and can further include non-coding regulatory sequences, and introns. Allelic variants of human and rat CARK include both functional and nonfunctional CARK proteins. Functional allelic variants are naturally occurring amino acid sequence variants ofthe human and rat CARK proteins that maintain the ability to bind a CARK ligand and/or modulate cellular mechanisms associated with cell growth or differentiation. Functional allelic variants will typically contain only conservative substitution of one or more amino acids of SEQ ID NO:2 or 8 or substitution, deletion or insertion of non-critical residues in non-critical regions of the protein. Non-functional allelic variants are naturally occurring amino acid sequence variants of the human and rat CARK proteins that do not have the ability to either bind a CARK ligand and/or modulate cellular mechanisms associated with cell growth or differentiation. Non-functional allelic variants will typically contain a non-conservative substitution, a deletion, or insertion or premature truncation of the amino acid sequence of SEQ ID NO:2 or 8, or a substitution, insertion or deletion in critical residues or critical regions. The present invention further provides non-human orthologues ofthe human CARK protein. Orthologues ofthe human CARK protein are proteins that are isolated from non-human organisms and possess the same CARK ligand binding and/or modulation of cellular mechanisms associated with cell growth or differentiation of the human CARK protein, e.g. the rat CARK protein (SEQ ID NO:8). Orthologues ofthe human CARK protein can readily be identified as comprising an amino acid sequence that is substantially homologous to SEQ ID NO:2 or 8. Moreover, nucleic acid molecules encoding other CARK family members and, thus, which have a nucleotide sequence which differs from the CARK sequences of SEQ ID NO: 1 , 3, 7. or 9. or the nucleotide sequence ofthe DNA insert ofthe plasmid deposited with ATCC as Accession Number are intended to be within the scope ofthe invention. For example, another CARK cDNA can be identified based on the nucleotide sequence of human or rat CARK. Moreover, nucleic acid molecules encoding CARK proteins from different species, and which, thus, have a nucleotide sequence which differs from the CARK sequences of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number are intended to be within the scope of the invention. For example, a mouse CARK cDNA can be identified based on the nucleotide sequence of a human or rat CARK. Nucleic acid molecules corresponding to natural allelic variants and homologues ofthe CARK cDNAs ofthe invention can be isolated based on their homology to the CARK nucleic acids disclosed herein using the cDNAs disclosed herein, or a portion thereof, as a hybridization probe according to standard hybridization techniques under stringent hybridization conditions. Nucleic acid molecules corresponding to natural allelic variants and homologues of the CARK cDNAs ofthe invention can further be isolated by mapping to the same chromosome or locus as the CARK gene. Accordingly, in another embodiment, an isolated nucleic acid molecule ofthe invention is at least 15. 20. 25, 30 or more nucleotides in length and hybridizes under stringent conditions to the nucleic acid molecule comprising the nucleotide sequence of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence ofthe DNA insert ofthe plasmid deposited with ATCC as Accession Number . In other embodiment, the nucleic acid is at least 30, 50, 100, 150, 200, 250, 300, 350, 400, 450, 467, 500, 550. 600, 650, 700, 750. 800, 850, 900, 950, 1000, 1500, 2000, 2500, or 2962 or more nucleotides in length. As used herein, the term "hybridizes under stringent conditions" is intended to describe conditions for hybridization and washing under which nucleotide sequences at least 60% homologous to each other typically remain hybridized to each other. Preferably, the conditions are such that sequences at least about 70%. more preferably at least about 80%>, even more preferably at least about 85%> or 90% homologous to each other typically remain hybridized to each other. Such stringent conditions are known to those skilled in the art and can be found in Current Protocols in Molecular Biology. John Wiley & Sons, N.Y. (1989), 6.3.1-6.3.6. A preferred, non-limiting example of stringent hybridization conditions are hybridization in 6X sodium chloride/sodium citrate (SSC) at about 45°C, followed by one or more washes in 0.2 X SSC, 0.1% SDS at 50°C. preferably at 55°C, more preferably at 60°C, and even more preferably at 65° C. Preferably, an isolated nucleic acid molecule of the invention that hybridizes under stringent conditions to the sequence of SEQ ID NOJ , 3, 7, or 9, corresponds to a naturally-occurring nucleic acid molecule. As used herein, a "naturally-occurring" nucleic acid molecule refers to an RNA or DNA molecule having a nucleotide sequence that occurs in nature (e.g., encodes a natural protein). In addition to naturally-occurring allelic variants ofthe CARK sequences that may exist in the population, the skilled artisan will further appreciate that changes can be introduced by mutation into the nucleotide sequences of SEQ ID NOJ , 3, 7, or 9, or the nucleotide sequence of the DNA insert ofthe plasmid deposited with ATCC as Accession Number . thereby leading to changes in the amino acid sequence ofthe encoded CARK proteins, without altering the functional ability ofthe CARK proteins. For example- nucleotide substitutions leading to amino acid substitutions at "non-essential" amino acid residues can be made in the sequence of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence ofthe DNA insert ofthe plasmid deposited with ATCC as Accession Number . A "non-essential" amino acid residue is a residue that can be altered from the wild-type sequence of CARK (e.g., the sequence of SEQ ID NO:2 or 8) without altering the biological activity, whereas an "essential" amino acid residue is required for biological activity. For example, amino acid residues that are conserved among the CARK proteins ofthe present invention, e.g., those present in the active site of the protein kinase domain, are predicted to be particularly unamenable to alteration. Furthermore, additional amino acid residues that are conserved between the CARK proteins of the present invention and other ankyrin repeat containing kinases are not likely to be amenable to alteration. Accordingly, another aspect ofthe invention pertains to nucleic acid molecules encoding CARK proteins that contain changes in amino acid residues that are not essential for activity. Such CARK proteins differ in amino acid sequence from SEQ ID NO:2 or 8, yet retain biological activity. In one embodiment, the isolated nucleic acid molecule comprises a nucleotide sequence encoding a protein, wherein the protein comprises an amino acid sequence at least about 50%o, 55%, 60%), 65%, 10%, 15%, 80%>, 85%, 90%, 92%, 95%, 98% or more homologous to SEQ ID NO:2 or 8. An isolated nucleic acid molecule encoding a CARK protein homologous to the protein of SEQ ID NO:2 or 8 can be created by introducing one or more nucleotide substitutions, additions or deletions into the nucleotide sequence of SEQ ID NOJ, 3. 7, or 9, or the nucleotide sequence of the DNA insert of the plasmid deposited with ATCC as Accession Number , such that one or more amino acid substitutions, additions or deletions are introduced into the encoded protein. Mutations can be introduced into SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence ofthe DNA insert ofthe plasmid deposited with ATCC as Accession Number by standard techniques, such as site- directed mutagenesis and PCR-mediated mutagenesis. Preferably, conservative amino acid substitutions are made at one or more predicted non-essential amino acid residues. A "conservative amino acid substitution" is one in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine. arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine. valine. leucine. isoleucine, proline. phenylalanine, methionine. tryptophan). beta- branched side chains (e.g.. threonine, valine. isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). Thus, a predicted nonessential amino acid residue in a CARK protein is preferably replaced with another amino acid residue from the same side chain family. Alternatively, in another embodiment, mutations can be introduced randomly along all or part of a CARK coding sequence, such as by saturation mutagenesis, and the resultant mutants can be screened for CARK biological activity to identify mutants that retain activity. Following mutagenesis of SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence ofthe DNA insert of the plasmid deposited with ATCC as Accession Number . the encoded protein can be expressed recombinantly and the activity ofthe protein can be determined. In a preferred embodiment, a mutant CARK protein can be assayed for the ability to 1) regulate transmission of signals from cellular receptors, e.g., cardiac cell growth factor receptors; 2) modulate the entry of cells, e.g., cardiac precursor cells, into mitosis; 3) modulate cellular differentiation; 4) modulate cell death; and 5) regulate cytoskeleton function, e.g.. actin bundling. In addition to the nucleic acid molecules encoding CARK proteins described above, another aspect ofthe invention pertains to isolated nucleic acid molecules which are antisense thereto. An "antisense" nucleic acid comprises a nucleotide sequence which is complementary to a "sense" nucleic acid encoding a protein, e.g.. complementary to the coding strand of a double-stranded cDNA molecule or complementary to an mRNA sequence. Accordingly, an antisense nucleic acid can hydrogen bond to a sense nucleic acid. The antisense nucleic acid can be complementary to an entire CARK coding strand, or to only a portion thereof. In one embodiment, an antisense nucleic acid molecule is antisense to a "coding region" ofthe coding strand of a nucleotide sequence encoding CARK. The term "coding region" refers to the region ofthe nucleotide sequence comprising codons which are translated into amino acid residues (e.g., the coding region of human CARK corresponds to SEQ ID NOJ. and the coding region of rat CARK corresponds to SEQ ID NO:9). In another embodiment, the antisense nucleic acid molecule is antisense to a "noncoding region" of the coding strand of a nucleotide sequence encoding CARK. The term "noncoding region" refers to 5' and 3' sequences which flank the coding region that are not translated into amino acids (i.e., also referred to as 5' and 3' untranslated regions). Given the coding strand sequences encoding CARK disclosed herein (e.g., SEQ ID NOJ or 9). antisense nucleic acids ofthe invention can be designed according to the rules of Watson and Crick base pairing. The antisense nucleic acid molecule can be complementary to the entire coding region of CARK mRNA, but more preferably is an oligonucleotide which is antisense to only a portion of the coding or noncoding region of CARK mRNA. For example, the antisense oligonucleotide can be complementary to the region surrounding the translation start site of CARK mRNA. An antisense oligonucleotide can be. for example, about 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50 nucleotides in length. An antisense nucleic acid of the invention can be constructed using chemical synthesis and enzymatic ligation reactions using procedures known in the art. For example, an antisense nucleic acid (e.g., an antisense oligonucleotide) can be chemically synthesized using naturally occurring nucleotides or variously modified nucleotides designed to increase the biological stability ofthe molecules or to increase the physical stability ofthe duplex formed between the antisense and sense nucleic acids, e.g., phosphorothioate derivatives and acridine substituted nucleotides can be used. Examples of modified nucleotides which can be used to generate the antisense nucleic acid include 5-fluorouracil. 5-bromouracil, 5-chlorouracil, 5-iodouracil, hypoxanthine, xantine, 4-acetylcytosine. 5-(carboxyhydroxylmethyl) uracil, 5- carboxymethylaminomethyl-2-thiouridine, 5-carboxymethylaminomethyluracil, dihydrouracil. beta-D-galactosylqueosine, inosine, N6-isopentenyladenine, 1- methylguanine. 1 -methylinosine, 2,2-dimethylguanine, 2-methyladenine, 2- methylguanine. 3-methylcytosine, 5-methylcytosine, N6-adenine, 7-methylguanine, 5- methylaminomethyluracil. 5-methoxyaminomethyl-2-thiouracil, beta-D- mannosylqueosine. 5'-methoxycarboxymethyluracil, 5-methoxyuracil, 2-methylthio-N6- isopentenyladenine. uracil-5-oxyacetic acid (v), wybutoxosine, pseudouracil. queosine, 2- thiocytosine. 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil, 5-methyluracil. uracil-5- oxyacetic acid methylester, uracil-5-oxyacetic acid (v), 5-methyl-2-thiouracil, 3-(3- amino-3-N-2-carboxypropyl) uracil, (acp3)w, and 2,6-diaminopurine. Alternatively, the antisense nucleic acid can be produced biologically using an expression vector into which a nucleic acid has been subcloned in an antisense orientation (i.e., RNA transcribed from the inserted nucleic acid will be of an antisense orientation to a target nucleic acid of interest, described further in the following subsection). The antisense nucleic acid molecules ofthe invention are typically administered to a subject or generated in situ such that they hybridize with or bind to cellular mRNA and/or genomic DNA encoding a CARK protein to thereby inhibit expression ofthe protein, e.g., by inhibiting transcription and/or translation. The hybridization can be by conventional nucleotide complementarity to form a stable duplex, or, for example, in the case of an antisense nucleic acid molecule which binds to DNA duplexes, through specific interactions in the major groove ofthe double helix. An example of a route of administration of antisense nucleic acid molecules ofthe invention include direct injection at a tissue site. Alternatively, antisense nucleic acid molecules can be modified to target selected cells and then administered systemically. For example, for systemic administration, antisense molecules can be modified such that they specifically bind to receptors or antigens expressed on a selected cell surface, e.g., by linking the antisense nucleic acid molecules to peptides or antibodies which bind to cell surface receptors or antigens. The antisense nucleic acid molecules can also be delivered to cells using the vectors described herein. To achieve sufficient intracellular concentrations of the antisense molecules, vector constructs in which the antisense nucleic acid molecule is placed under the control of a strong pol II or pol III promoter are preferred. In yet another embodiment, the antisense nucleic acid molecule ofthe invention is an α-anomeric nucleic acid molecule. An α-anomeric nucleic acid molecule forms specific double-stranded hybrids with complementary RNA in which, contrary to the usual β-units, the strands run parallel to each other (Gaultier et al. (1987) Nucleic Acids. Res. 15:6625-6641). The antisense nucleic acid molecule can also comprise a 2'-o- methylribonucleotide (Inoue et al. (1987) Nucleic Acids Res. 15:6131 -6148) or a chimeric RNA-DNA analogue (Inoue et al. (1987) FEBS Lett. 215:327-330). In still another embodiment, an antisense nucleic acid of the invention is a ribozyme. Ribozymes are catalytic RNA molecules with ribonuclease activity which are capable of cleaving a single-stranded nucleic acid, such as an mRNA. to which they have a complementary region. Thus, ribozymes (e.g., hammerhead ribozymes (described in Haselhoff and Gerlach (1988) Nature 334:585-591)) can be used to catalytically cleave CARK mRNA transcripts to thereby inhibit translation of CARK mRNA. A ribozyme having specificity for a CARK-encoding nucleic acid can be designed based upon the nucleotide sequence of a CARK cDNA disclosed herein (i.e., SEQ ID NOJ, 3, 7, or 9, or the nucleotide sequence ofthe DNA insert ofthe plasmid deposited with ATCC as Accession Number ). For example, a derivative of a Tetrahymena L-19 IVS RNA can be constructed in which the nucleotide sequence ofthe active site is complementary to the nucleotide sequence to be cleaved in a CARK- encoding mRNA. See, e.g.. Cech et al. U.S. Patent No. 4,987,071 ; and Cech et al. U.S. Patent No. 5J 16,742. Alternatively, CARK mRNA can be used to select a catalytic RNA having a specific ribonuclease activity from a pool of RNA molecules. See, e.g., Bartel, D. and Szostak, J.W. (1993) Science 261 :141 1-1418. Alternatively, CARK gene expression can be inhibited by targeting nucleotide sequences complementary to the regulatory region of the CARK gene (e.g.. the CARK promoter and/or enhancers) to form triple helical structures that prevent transcription of the CARK gene in target cells. See generally. Helene, C. (1991) Anticancer Drug Des. 6(6):569-84; Helene, C. et al. (1992) Ann. N Y. Acad. Sci. 660:27-36; and Maher, LJ. (1992) Bioassays 14(12):807-15. In yet another embodiment, the CARK nucleic acid molecules ofthe present invention can be modified at the base moiety, sugar moiety or phosphate backbone to improve, e.g., the stability, hybridization, or solubility of the molecule. For example, the deoxyribose phosphate backbone ofthe nucleic acid molecules can be modified to generate peptide nucleic acids (see Hyrup B. et al. (1996) Bioor ganic & Medicinal Chemistry 4 (1): 5-23). As used herein, the terms "peptide nucleic acids" or "PNAs" refer to nucleic acid mimics, e.g., DNA mimics, in which the deoxyribose phosphate backbone is replaced by a pseudopeptide backbone and only the four natural nucleobases are retained. The neutral backbone of PNAs has been shown to allow for specific hybridization to DNA and RNA under conditions of low ionic strength. The synthesis of PNA oligomers can be performed using standard solid phase peptide synthesis protocols as described in Hyrup B. et al. (1996) supra; Perry-O'Keefe et al. Proc. Natl. Acad. Sci. 93: 14670-675. PNAs of CARK nucleic acid molecules can be used in therapeutic and diagnostic applications. For example. PNAs can be used as antisense or antigene agents for sequence-specific modulation of gene expression by, for example, inducing transcription or translation arrest or inhibiting replication. PNAs of CARK nucleic acid molecules can also be used in the analysis of single base pair mutations in a gene, (e.g., by PNA- directed PCR clamping): as 'artificial restriction enzymes' when used in combination with other enzymes, (e.g.. SI nucleases (Hyrup B. (1996) supra)); or as probes or primers for DNA sequencing or hybridization (Hyrup B. et al. (1996) supra; Perry- O'Keefe supra). In another embodiment, PNAs of CARK can be modified, (e.g., to enhance their stability or cellular uptake), by attaching lipophilic or other helper groups to PNA, by the formation of PNA-DNA chimeras, or by the use of liposomes or other techniques of drug delivery known in the art. For example. PNA-DNA chimeras of CARK nucleic acid molecules can be generated which may combine the advantageous properties of PNA and DNA. Such chimeras allow DNA recognition enzymes, (e.g., RNAse H and DNA polymerases), to interact with the DNA portion while the PNA portion would provide high binding affinity and specificity. PNA-DNA chimeras can be linked using linkers of appropriate lengths selected in terms of base stacking, number of bonds between the nucleobases. and orientation (Hyrup B. (1996) supra). The synthesis of PNA-DNA chimeras can be performed as described in Hyrup B. (1996) supra and Finn P.J. et al. (1996) Nucleic Acids Res. 24 (17): 3357-63. For example, a DNA chain can be synthesized on a solid support using standard phosphoramidite coupling chemistry and modified nucleoside analogs, e.g., 5'-(4-methoxytrityl)amino-5'-deoxy-thymidine phosphoramidite. can be used as a between the PNA and the 5' end of DNA (Mag, M. et al. (1989) Nucleic Acid Res. 17: 5973-88). PNA monomers are then coupled in a stepwise manner to produce a chimeric molecule with a 5' PNA segment and a 3' DNA segment (Finn P.J. et al. (1996) supra). Alternatively, chimeric molecules can be synthesized with a 5' DNA segment and a 3' PNA segment (Peterser, K.H. et al. (1975) Bioor ganic Med. Chem. Lett. 5: 1 1 19-11 124). In other embodiments, the oligonucleotide may include other appended groups such as peptides (e.g., for targeting host cell receptors in vivo), or agents facilitating transport across the cell membrane (see, e.g., Letsinger et al. (1989) Proc. Natl. Acad. Sci. USA 86:6553-6556: Lemaitre et al. (1987) Proc. Natl. Acad. Sci. USA 84:648-652; PCT Publication No. W088/09810) or the blood-brain barrier (see, e.g., PCT Publication No. W089/10134). In addition, oligonucleotides can be modified with hybridization- triggered cleavage agents (See, e.g., Krol et al. (1988) Bio-Techniques 6:958-976) or intercalating agents. (See, e.g., Zon (1988) Pharm. Res. 5:539-549). To this end, the oligonucleotide may be conjugated to another molecule, (e.g., a peptide, hybridization triggered cross-linking agent, transport agent, or hybridization-triggered cleavage agent). II. Isolated CARK Proteins and Anti-CARK Antibodies One aspect ofthe invention pertains to isolated CARK proteins, and biologically active portions thereof, as well as polypeptide fragments suitable for use as immunogens to raise anti-CARK antibodies. In one embodiment, native CARK proteins can be isolated from cells or tissue sources by an appropriate purification scheme using standard protein purification techniques. In another embodiment, CARK proteins are produced by recombinant DNA techniques. Alternative to recombinant expression, a CARK protein or polypeptide can be synthesized chemically using standard peptide synthesis techniques. An "isolated" or "purified" protein or biologically active portion thereof is substantially free of cellular material or other contaminating proteins from the cell or tissue source from which the CARK protein is derived, or substantially free from chemical precursors or other chemicals when chemically synthesized. The language "substantially free of cellular material" includes preparations of CARK protein in which the protein is separated from cellular components ofthe cells from which it is isolated or recombinantly produced. In one embodiment, the language "substantially free of cellular material" includes preparations of CARK protein having less than about 30%o (by dry weight) of non-CARK protein (also referred to herein as a "contaminating protein"), more preferably less than about 20%> of non-CARK protein, still more preferably less than about 10%> of non-CARK protein, and most preferably less than about 5% non-CARK protein. When the CARK protein or biologically active portion thereof is recombinantly produced, it is also preferably substantially free of culture medium, i.e., culture medium represents less than about 20%). more preferably less than about 10%), and most preferably less than about 5%> of the volume ofthe protein preparation. The language "substantially free of chemical precursors or other chemicals" includes preparations of CARK protein in which the protein is separated from chemical precursors or other chemicals which are involved in the synthesis ofthe protein. In one embodiment, the language "substantially free of chemical precursors or other chemicals" includes preparations of CARK protein having less than about 30% (by dry weight) of chemical precursors or non-CARK chemicals, more preferably less than about 20% chemical precursors or non-CARK chemicals, still more preferably less than about 10% chemical precursors or non-CARK chemicals, and most preferably less than about 5% chemical precursors or non-CARK chemicals. As used herein, a "biologically active portion" of a CARK protein includes a fragment of a CARK protein which participates in an interaction between a CARK molecule and a non-CARK molecule. Biologically active portions of a CARK protein include peptides comprising amino acid sequences sufficiently homologous to or derived from the amino acid sequence ofthe CARK protein, e.g., the amino acid sequence shown in SEQ ID NO:2 or 8, which include less amino acids than the full length CARK proteins, and exhibit at least one activity of a CARK protein. Typically, biologically active portions comprise a domain or motif with at least one activity of the CARK protein, e.g., modulating signaling pathways associated with cellular growth and differentiation. A biologically active portion of a CARK protein can be a polypeptide which is, for example, 10, 25, 50, 100, 200 or more amino acids in length. Biologically active portions of a CARK protein can be used as targets for developing agents which modulate a CARK mediated activity, e.g., the modulation of signaling pathways associated with cellular growth and differentiation. In one embodiment, a biologically active portion of a CARK protein comprises at least one ankyrin repeat domain, and/or at least one protein kinase domain. It is to be understood that a preferred biologically active portion of a CARK protein of the present invention may contain at least one ankyrin repeat domain. Another preferred biologically active portion of a CARK protein may contain at least two, three, four, five, six, seven, eight, or nine ankyrin repeat domains. Yet another preferred biologically active portion of a CARK protein may contain at least one protein kinase domain. Moreover, other biologically active portions, in which other regions of the protein are deleted, can be prepared by recombinant techniques and evaluated for one or more ofthe functional activities of a native CARK protein. In a preferred embodiment, the CARK protein has an amino acid sequence shown in SEQ ID NO:2 or 8. In other embodiments, the CARK protein is substantially homologous to SEQ ID NO:2 or 8, and retains the functional activity of the protein of SEQ ID NO:2 or 8, yet differs in amino acid sequence due to natural allelic variation or mutagenesis, as described in detail in subsection I above. Accordingly, in another embodiment, the CARK protein is a protein which comprises an amino acid sequence at least about 50%, 55%, 60%, 65%, 70%, 75%. 80%, 85%, 90%, 95%, 98% or more homologous to SEQ ID NO:2 or 8. To determine the percent identity of two amino acid sequences or of two nucleic acid sequences, the sequences are aligned for optimal comparison puφoses (e.g., gaps can be introduced in one or both of a first and a second amino acid or nucleic acid sequence for optimal alignment and non-homologous sequences can be disregarded for comparison puφoses). In a preferred embodiment, the length of a reference sequence aligned for comparison puφoses is at least 30%>, preferably at least 40%, more preferably at least 50%o. even more preferably at least 60%, and even more preferably at least 70%, 80%>, or 90% ofthe length of the reference sequence (e.g., when aligning a second sequence to the CARK amino acid sequence of SEQ ID NO:2 having 835 amino acid residues, at least 251. preferably at least 334, more preferably at least 418, even more preferably at least 501. and even more preferably at least 585. 668 or 752 amino acid residues are aligned). The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position (as used herein amino acid or nucleic acid "identity" is equivalent to amino acid or nucleic acid "homology"). The percent identity between the two sequences is a function of the number of identical positions shared by the sequences, taking into account the number of gaps, and the length of each gap, which need to be introduced for optimal alignment ofthe two sequences. The comparison of sequences and determination of percent identity between two sequences can be accomplished using a mathematical algorithm. In a preferred embodiment, the percent identity between two amino acid sequences is determined using the Needleman and Wunsch (J. Mol. Biol. (48):444-453 (1970)) algorithm which has been incoφorated into the GAP program in the GCG software package (available at http://www.gcg.com). using either a Blossom 62 matrix or a PAM250 matrix, and a gap weight of 16, 14. 12. 10. 8. 6, or 4 and a length weight of 1 , 2, 3. 4. 5, or 6. In yet another preferred embodiment, the percent identity between two nucleotide sequences is determined using the GAP program in the GCG software package (available at http://www.gcg.com). using a NWSgapdna.CMP matrix and a gap weight of 40, 50, 60, 70, or 80 and a length weight of 1 , 2, 3, 4, 5. or 6. In another embodiment, the percent identity between two amino acid or nucleotide sequences is determined using the algorithm of E. Meyers and W. Miller (CABIOS, 4: 1 1-17 (1989)) which has been incoφorated into the ALIGN program (version 2.0), using a PAM120 weight residue table, a gap length penalty of 12 and a gap penalty of 4. The nucleic acid and protein sequences ofthe present invention can further be used as a "query sequence" to perform a search against public databases to, for example, identify other family members or related sequences. Such searches can be performed using the NBLAST and XBLAST programs (version 2.0) of Altschul. et al. (1990) J. Mol. Biol. 215:403-10. BLAST nucleotide searches can be performed with the NBLAST program, score = 100, wordlength = 12 to obtain nucleotide sequences homologous to CARK nucleic acid molecules ofthe invention. BLAST protein searches can be performed with the XBLAST program- score = 50. wordlength = 3 to obtain amino acid sequences homologous to CARK protein molecules of the invention. To obtain gapped alignments for comparison puφoses, Gapped BLAST can be utilized as described in Altschul et al.. (1997) Nucleic Acids Res. 25(17):3389-3402. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. See http://www.ncbi.nlm.nih.gov. The invention also provides CARK chimeric or fusion proteins. As used herein, a CARK "chimeric protein" or "fusion protein" comprises a CARK polypeptide operatively linked to a non-CARK polypeptide. An "CARK polypeptide" refers to a polypeptide having an amino acid sequence corresponding to CARK, whereas a "non- CARK polypeptide" refers to a polypeptide having an amino acid sequence corresponding to a protein which is not substantially homologous to the CARK protein, e.g., a protein which is different from the CARK protein and which is derived from the same or a different organism. Within a CARK fusion protein the CARK polypeptide can correspond to all or a portion of a CARK protein. In a preferred embodiment, a CARK fusion protein comprises at least one biologically active portion of a CARK protein. In another preferred embodiment, a CARK fusion protein comprises at least two biologically active portions of a CARK protein. Within the fusion protein, the term "operatively linked" is intended to indicate that the CARK polypeptide and the non- CARK polypeptide are fused in-frame to each other. The non-CARK polypeptide can be fused to the N-terminus or C-terminus of the CARK polypeptide. For example, in one embodiment, the fusion protein is a GST-CARK fusion protein in which the CARK sequences are fused to the C-terminus ofthe GST sequences. Such fusion proteins can facilitate the purification of recombinant CARK. In another embodiment, the fusion protein is a CARK protein containing a heterologous signal sequence at its N-terminus. In certain host cells (e.g., mammalian host cells), expression and/or secretion of CARK can be increased through use of a heterologous signal sequence. The CARK fusion proteins of the invention can be incorporated into pharmaceutical compositions and administered to a subject in vivo. The CARK fusion proteins can be used to affect the bioavailability of a CARK substrate. Use of CARK fusion proteins may be useful therapeutically for the treatment of disorders caused by, for example, (i) aberrant modification or mutation of a gene encoding a CARK protein; (ii) mis-regulation of the CARK gene; and (iii) aberrant post-translational modification of a CARK protein. Moreover, the CARK- fusion proteins of the invention can be used as immunogens to produce anti-CARK antibodies in a subject, to purify CARK ligands and in screening assays to identify molecules which inhibit the interaction of CARK with a CARK substrate. Preferably, a CARK chimeric or fusion protein of the invention is produced by standard recombinant DNA techniques. For example, DNA fragments coding for the different polypeptide sequences are ligated together in-frame in accordance with conventional techniques, for example by employing blunt-ended or stagger-ended termini for ligation, restriction enzyme digestion to provide for appropriate termini, filling-in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and enzymatic ligation. In another embodiment, the fusion gene can be synthesized by conventional techniques including automated DNA synthesizers. Alternatively, PCR amplification of gene fragments can be carried out using anchor primers which give rise to complementary overhangs between two consecutive gene fragments which can subsequently be annealed and reamplified to generate a chimeric gene sequence (see, for example, Current Protocols in Molecular Biology, eds. Ausubel et al. John Wiley & Sons: 1992). Moreover, many expression vectors are commercially available that already encode a fusion moiety (e.g., a GST polypeptide). A CARK- encoding nucleic acid can be cloned into such an expression vector such that the fusion moiety is linked in-frame to the CARK protein. The present invention also pertains to variants of the CARK proteins which function as either CARK agonists (mimetics) or as CARK antagonists. Variants ofthe CARK proteins can be generated by mutagenesis, e.g., discrete point mutation or truncation of a CARK protein. An agonist of the CARK proteins can retain substantially the same, or a subset, ofthe biological activities of the naturally occurring form of a CARK protein. An antagonist of a CARK protein can inhibit one or more of the activities ofthe naturally occurring form ofthe CARK protein by, for example, competitively modulating a CARK-mediated activity of a CARK protein. Thus, specific biological effects can be elicited by treatment with a variant of limited function. In one embodiment, treatment of a subject with a variant having a subset of the biological activities of the naturally occurring form of the protein has fewer side effects in a subject relative to treatment with the naturally occurring form ofthe CARK protein. In one embodiment, variants of a CARK protein which function as either CARK agonists (mimetics) or as CARK antagonists can be identified by screening combinatorial libraries of mutants, e.g., truncation mutants, of a CARK protein for CARK protein agonist or antagonist activity. In one embodiment, a variegated library of CARK variants is generated by combinatorial mutagenesis at the nucleic acid level and is encoded by a variegated gene library. A variegated library of CARK variants can be produced by, for example, enzymatically ligating a mixture of synthetic oligonucleotides into gene sequences such that a degenerate set of potential CARK sequences is expressible as individual polypeptides, or alternatively, as a set of larger fusion proteins (e.g., for phage display) containing the set of CARK sequences therein. There are a variety of methods which can be used to produce libraries of potential CARK variants from a degenerate oligonucleotide sequence. Chemical synthesis of a degenerate gene sequence can be performed in an automatic DNA synthesizer, and the synthetic gene then ligated into an appropriate expression vector. Use of a degenerate set of genes allows for the provision, in one mixture, of all of the sequences encoding the desired set of potential CARK sequences. Methods for synthesizing degenerate oligonucleotides are known in the art (see. e.g., Narang, S.A. (1983) Tetrahedron 39:3; Itakura et al. (1984) Annu. Rev. Biochem. 53:323; Itakura et al. (1984) Science 198: 1056; Ike et al. (1983) Nucleic Acid Res. 11 :477. In addition, libraries of fragments of a CARK protein coding sequence can be used to generate a variegated population of CARK fragments for screening and subsequent selection of variants of a CARK protein. In one embodiment, a library of coding sequence fragments can be generated by treating a double stranded PCR fragment of a CARK coding sequence with a nuclease under conditions wherein nicking occurs only about once per molecule, denaturing the double stranded DNA. renaturing the DNA to form double stranded DNA which can include sense/antisense pairs from different nicked products, removing single stranded portions from reformed duplexes by treatment with SI nuclease. and ligating the resulting fragment library into an expression vector. By this method, an expression library can be derived which encodes N-terminal, C-terminal and internal fragments of various sizes ofthe CARK protein. Several techniques are known in the art for screening gene products of combinatorial libraries made by point mutations or truncation, and for screening cDNA libraries for gene products having a selected property. Such techniques are adaptable for rapid screening ofthe gene libraries generated by the combinatorial mutagenesis of CARK proteins. The most widely used techniques, which are amenable to high throughput analysis, for screening large gene libraries typically include cloning the gene library into replicable expression vectors, transforming appropriate cells with the resulting library of vectors, and expressing the combinatorial genes under conditions in which detection of a desired activity facilitates isolation of the vector encoding the gene whose product was detected. Recrusive ensemble mutagenesis (REM), a new technique which enhances the frequency of functional mutants in the libraries, can be used in combination with the screening assays to identify CARK variants (Arkin and Yourvan (1992) Proc. Natl. Acad. Sci. USA 59:781 1-7815; Delgrave et al. (1993) Protein Engineering 6(3):327-331). In one embodiment, cell based assays can be exploited to analyze a variegated CARK library. For example, a library of expression vectors can be transfected into a cell line, e.g., a cardiac cell line, which ordinarily responds to a particular ligand in a CARK-dependent manner. The transfected cells are then contacted with the ligand and the effect of expression ofthe mutant on signaling by the ligand can be detected, e.g., by monitoring intracellular calcium, IP3, or diacylglycerol concentration, phosphorylation profile of intracellular proteins, cell proliferation and/or migration, or the activity of a CARK-regulated transcription factor. Plasmid DNA can then be recovered from the cells which score for inhibition, or alternatively, potentiation of signaling by the ligand, and the individual clones further characterized. An isolated CARK protein, or a portion or fragment thereof, can be used as an immunogen to generate antibodies that bind CARK using standard techniques for polyclonal and monoclonal antibody preparation. A full-length CARK protein can be used or, alternatively, the invention provides antigenic peptide fragments of CARK for use as immunogens. The antigenic peptide of CARK comprises at least 8 amino acid residues ofthe amino acid sequence shown in SEQ ID NO:2 or 8 and encompasses an epitope of CARK such that an antibody raised against the peptide forms a specific immune complex with CARK. Preferably, the antigenic peptide comprises at least 10 amino acid residues, more preferably at least 15 amino acid residues, even more preferably at least 20 amino acid residues, and most preferably at least 30 amino acid residues. Preferred epitopes encompassed by the antigenic peptide are regions of CARK that are located on the surface ofthe protein, e.g., hydrophilic regions, as well as regions with high antigenicity (see, for example, Figure 2). A CARK immunogen typically is used to prepare antibodies by immunizing a suitable subject, (e.g., rabbit, goat, mouse or other mammal) with the immunogen. An appropriate immunogenic preparation can contain, for example, recombinantly expressed CARK protein or a chemically synthesized CARK polypeptide. The preparation can further include an adjuvant, such as Freund's complete or incomplete adjuvant, or similar immunostimulatory agent. Immunization of a suitable subject with an immunogenic CARK preparation induces a polyclonal anti-CARK antibody response. Accordingly, another aspect ofthe invention pertains to anti-CARK antibodies. The term "antibody" as used herein refers to immunoglobulin molecules and immunologically active portions of immunoglobulin molecules, i.e., molecules that contain an antigen binding site which specifically binds (immunoreacts with) an antigen, such as CARK. Examples of immunologically active portions of immunoglobulin molecules include F(ab) and F(ab') 2 fragments which can be generated by treating the antibody with an enzyme such as pepsin. The invention provides polyclonal and monoclonal antibodies that bind CARK. The term "monoclonal antibody" or "monoclonal antibody composition", as used herein, refers to a population of antibody molecules that contain only one species of an antigen binding site capable of immunoreacting with a particular epitope of CARK. A monoclonal antibody composition thus typically displays a single binding affinity for a particular CARK protein with which it immunoreacts. Polyclonal anti-CARK antibodies can be prepared as described above by immunizing a suitable subject with a CARK immunogen. The anti-CARK antibody titer in the immunized subject can be monitored over time by standard techniques, such as with an enzyme linked immunosorbent assay (ELISA) using immobilized CARK. If desired, the antibody molecules directed against CARK can be isolated from the mammal (e.g., from the blood) and further purified by well known techniques, such as protein A chromatography to obtain the IgG fraction. At an appropriate time after immunization, e.g., when the anti-CARK antibody titers are highest, antibody-producing cells can be obtained from the subject and used to prepare monoclonal antibodies by standard techniques, such as the hybridoma technique originally described by Kohler and Milstein (1975) Nature 256:495-497) (see also, Brown et al. (1981) . Immunol. 127:539-46; Brown et al. (1980) . Biol. Chem .255:4980-83; Yeh et al. (1976) Proc. Natl. Acad. Sci. USA 76:2927-31; and Yeh et al. (1982) Int. J. Cancer 29:269-75), the more recent human B cell hybridoma technique (Kozbor et al. (1983) Immunol Today 4:72), the EBV-hybridoma technique (Cole et al. (1985), Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96) or trioma techniques. The technology for producing monoclonal antibody hybridomas is well known (see generally R. H. Kenneth, in Monoclonal Antibodies: A New Dimension In Biological Analyses, Plenum Publishing Coφ., New York, New York (1980); E. A. Lerner (1981) Yale J. Biol. Med, 54:387-402; M. L. Gefter et al. (1977) Somatic Cell Genet. 3:231-36). Briefly, an immortal cell line (typically a myeloma) is fused to lymphocytes (typically splenocytes) from a mammal immunized with a CARK immunogen as described above, and the culture supernatants ofthe resulting hybridoma cells are screened to identify a hybridoma producing a monoclonal antibody that binds CARK. Any ofthe many well known protocols used for fusing lymphocytes and immortalized cell lines can be applied for the puφose of generating an anti-CARK monoclonal antibody (see, e.g., G. Galfre et al. (1977) Nature 266:55052; Gefter et al. Somatic Cell Genet., cited supra; Lerner, Yale J. Biol. Med., cited supra; Kenneth, Monoclonal Antibodies, cited supra). Moreover, the ordinarily skilled worker will appreciate that there are many variations of such methods which also would be useful. Typically, the immortal cell line (e.g., a myeloma cell line) is derived from the same mammalian species as the lymphocytes. For example, murine hybridomas can be made by fusing lymphocytes from a mouse immunized with an immunogenic preparation of the present invention with an immortalized mouse cell line. Preferred immortal cell lines are mouse myeloma cell lines that are sensitive to culture medium containing hypoxanthine, aminopterin and thymidine ("HAT medium"). Any of a number of myeloma cell lines can be used as a fusion partner according to standard techniques, e.g., the P3-NSl/l-Ag4-l. P3-x63-Ag8.653 or Sp2/O-Agl4 myeloma lines. These myeloma lines are available from ATCC. Typically, HAT-sensitive mouse myeloma cells are fused to mouse splenocytes using polyethylene glycol ("PEG"). Hybridoma cells resulting from the fusion are then selected using HAT medium, which kills unfused and unproductively fused myeloma cells (unfused splenocytes die after several days because they are not transformed). Hybridoma cells producing a monoclonal antibody of the invention are detected by screening the hybridoma culture supernatants for antibodies that bind CARK, e.g., using a standard ELISA assay. Alternative to preparing monoclonal antibody-secreting hybridomas, a monoclonal anti-CARK antibody can be identified and isolated by screening a recombinant combinatorial immunoglobulin library (e.g., an antibody phage display library) with CARK to thereby isolate immunoglobulin library members that bind CARK. Kits for generating and screening phage display libraries are commercially available (e.g., the Phannacia Recombinant Phage Antibody System, Catalog No. 27- 9400-01; and the Stratagene Sur/ZAP™ Phage Display Kit, Catalog No. 240612). Additionally, examples of methods and reagents particularly amenable for use in generating and screening antibody display library can be found in. for example, Ladner et al. U.S. Patent No. 5.223J09; Kang et al. PCT International Publication No. WO 92/18619; Dower et al. PCT International Publication No. WO 91/17271 ; Winter et al. PCT International Publication WO 92/20791 ; Markland et al. PCT International Publication No. WO 92/15679; Breitling et al. PCT International Publication WO 93/01288; McCafferty et al. PCT International Publication No. WO 92/01047; Garrard et al. PCT International Publication No. WO 92/09690; Ladner et al. PCT International Publication No. WO 90/02809; Fuchs et al. (1991) Bio/Technology 9: 1370-1372; Hay et al. (1992) Hum. Antibod. Hybridomas 3:81-85; Huse et al. (1989) Science 246: 1275- 1281; Griffiths et al. (1993) EMBO J 12:725-734; Hawkins et al. (1992) J. Mol. Biol. 226:889-896; Clarkson et al. (1991) Nature 352:624-628; Gram et al. (1992) Proc. Natl. Acad. Sci. USA 89:3576-3580; Garrad et al. (1991) Bio/Technology 9: 1373-1377; Hoogenboom et 7/. (1991) Nwc. Acid Res. 19:4133-4137; Barbas et al. (1991) Proc. Natl. Acad. Sci. USA 88:7978-7982; and McCafferty et al. Nature (1990) 348:552-554. Additionally, recombinant anti-CARK antibodies, such as chimeric and humanized monoclonal antibodies, comprising both human and non-human portions, which can be made using standard recombinant DΝA techniques, are within the scope of the invention. Such chimeric and humanized monoclonal antibodies can be produced by recombinant DΝA techniques known in the art, for example using methods described in Robinson et al. International Application No. PCT/US86/02269; Akira, et al. European Patent Application 184.187; Taniguchi, M.. European Patent Application 171 ,496; Morrison et al. European Patent Application 173,494; Neuberger et al. PCT International Publication No. WO 86/01533; Cabilly et al. U.S. Patent No. 4,816,567; Cabilly et al. European Patent Application 125,023; Better et al. (1988) Science 240:1041-1043: Liu et al. (1987) Proc. Natl. Acad. Sci. USA 84:3439-3443; Liu et al. (1987) . Immunol. 139:3521-3526; Sun et al. (1987) Proc. Natl. Acad. Sci. USA 84:214-218; Nishimura et al. (1987) Cane. Res. 47:999-1005; Wood et al. (1985) Nature 314:446-449; and Shaw et al. (1988) J. Natl. Cancer Inst. 80:1553-1559); Morrison, S. L. (1985) Science 229:1202-1207; Oi et al. (1986) BioTechniques 4:214; Winter U.S. Patent 5.225.539; Jones et al. (1986) Nature 321 :552-525; Verhoeyan et al. (1988) Science 239:1534: and Beidler et α/. (1988) J. Immunol. 141 :4053-4060. An anti-CARK antibody (e.g., monoclonal antibody) can be used to isolate CARK by standard techniques, such as affinity chromatography or immunoprecipitation. An anti-CARK antibody can facilitate the purification of natural CARK from cells and of recombinantly produced CARK expressed in host cells. Moreover, an anti-CARK antibody can be used to detect CARK protein (e.g., in a cellular lysate or cell supernatant) in order to evaluate the abundance and pattern of expression ofthe CARK protein. Anti-CARK antibodies can be used diagnostically to monitor protein levels in tissue as part of a clinical testing procedure, e.g., to, for example, determine the efficacy of a given treatment regimen. Detection can be facilitated by coupling (i.e., physically linking) the antibody to a detectable substance. Examples of detectable substances include various enzymes, prosthetic groups, fluorescent materials, luminescent materials, bioluminescent materials, and radioactive materials. Examples of suitable enzymes include horseradish peroxidase, alkaline phosphatase, -galactosidase, or acetylcholinesterase; examples of suitable prosthetic group complexes include streptavidin/biotin and avidin/biotin; examples of suitable fluorescent materials include umbelliferone, fluorescein, fluorescein isothiocyanate, rhodamine, dichlorotriazinylamine fluorescein, dansyl chloride or phycoerythrin; an example of a luminescent material includes luminol; examples of bioluminescent materials include luciferase. luciferin, and aequorin, and examples of suitable radioactive material include 125 I, 13 , I, 35 S or 3 H. III. Recombinant Expression Vectors and Host Cells Another aspect ofthe invention pertains to vectors, preferably expression vectors, containing a nucleic acid encoding a CARK protein (or a portion thereof). As used herein, the term "vector" refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of vector is a "plasmid", which refers to a circular double stranded DNA loop into which additional DNA segments can be ligated. Another type of vector is a viral vector, wherein additional DNA segments can be ligated into the viral genome. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g., bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) are integrated into the genome of a host cell upon introduction into the host cell, and thereby are replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes to which they are operatively linked. Such vectors are referred to herein as "expression vectors". In general, expression vectors of utility in recombinant DNA techniques are often in the form of plasmids. In the present specification, "plasmid" and "vector" can be used interchangeably as the plasmid is the most commonly used form of vector. However, the invention is intended to include such other forms of expression vectors. such as viral vectors (e.g.. replication defective retroviruses, adenoviruses and adeno- associated viruses), which serve equivalent functions. The recombinant expression vectors ofthe invention comprise a nucleic acid of the invention in a form suitable for expression of the nucleic acid in a host cell, which means that the recombinant expression vectors include one or more regulatory sequences, selected on the basis of the host cells to be used for expression, which is operatively linked to the nucleic acid sequence to be expressed. Within a recombinant expression vector, "operably linked" is intended to mean that the nucleotide sequence of interest is linked to the regulatory sequence(s) in a manner which allows for expression ofthe nucleotide sequence (e.g., in an in vitro transcription/translation system or in a host cell when the vector is introduced into the host cell). The term "regulatory sequence" is intended to include promoters, enhancers and other expression control elements (e.g., polyadenylation signals). Such regulatory sequences are described, for example, in Goeddel; Gene Expression Technology: Methods in Enzymology 185, Academic Press. San Diego, CA (1990). Regulatory sequences include those which direct constitutive expression of a nucleotide sequence in many types of host cells and those which direct expression ofthe nucleotide sequence only in certain host cells (e.g., tissue-specific regulatory sequences). It will be appreciated by those skilled in the art that the design of the expression vector can depend on such factors as the choice of the host cell to be transformed, the level of expression of protein desired, and the like. The expression vectors of the invention can be introduced into host cells to thereby produce proteins or peptides. including fusion proteins or peptides, encoded by nucleic acids as described herein (e.g.. CARK proteins, mutant forms of CARK proteins, fusion proteins, and the like). The recombinant expression vectors of the invention can be designed for expression of CARK proteins in prokaryotic or eukaryotic cells. For example, CARK proteins can be expressed in bacterial cells such as E. coli, insect cells (using baculovirus expression vectors) yeast cells or mammalian cells. Suitable host cells are discussed further in Goeddel, Gene Expression Technology: Methods in Enzymology 185, Academic Press. San Diego, CA (1990). Alternatively, the recombinant expression vector can be transcribed and translated in vitro, for example using T7 promoter regulatory sequences and T7 polymerase. Expression of proteins in prokaryotes is most often carried out in E. coli with vectors containing constitutive or inducible promoters directing the expression of either fusion or non-fusion proteins. Fusion vectors add a number of amino acids to a protein encoded therein, usually to the amino terminus ofthe recombinant protein. Such fusion vectors typically serve three puφoses: 1) to increase expression of recombinant protein; 2) to increase the solubility ofthe recombinant protein; and 3) to aid in the purification ofthe recombinant protein by acting as a ligand in affinity purification. Often, in fusion expression vectors, a proteolytic cleavage site is introduced at the junction ofthe fusion moiety and the recombinant protein to enable separation ofthe recombinant protein from the fusion moiety subsequent to purification ofthe fusion protein. Such enzymes, and their cognate recognition sequences, include Factor Xa, thrombin and enterokinase. Typical fusion expression vectors include pGEX (Pharmacia Biotech Inc; Smith, D.B. and Johnson, K.S. (1988) Gene 67:31 -40), pMAL (New England Biolabs, Beverly, MA) and pRIT5 (Pharmacia, Piscataway, NJ) which fuse glutathione S-transferase (GST), maltose E binding protein, or protein A, respectively, to the target recombinant protein. Purified fusion proteins can be utilized in CARK activity assays, (e.g.. direct assays or competitive assays described in detail below), or to generate antibodies specific for CARK proteins, for example. In a preferred embodiment, a CARK fusion protein expressed in a retroviral expression vector of the present invention can be utilized to infect bone marrow cells which are subsequently transplanted into irradiated recipients. The pathology ofthe subject recipient is then examined after sufficient time has passed (e.g.. six (6) weeks). Examples of suitable inducible non-fusion E. coli expression vectors include pTrc (Amann et al., (1988) Gene 69:301-315) and pET l id (Studier et al.. Gene Expression Technology: Methods in Enzymology 185, Academic Press. San Diego. California (1990) 60-89). Target gene expression from the pTrc vector relies on host RNA polymerase transcription from a hybrid tφ-lac fusion promoter. Target gene expression from the pET 1 Id vector relies on transcription from a T7 gnlO-lac fusion promoter mediated by a coexpressed viral RNA polymerase (T7 gnl). This viral polymerase is supplied by host strains BL21(DE3) or HMS174(DE3) from a resident prophage harboring a T7 gnl gene under the transcriptional control ofthe lacUV 5 promoter. One strategy to maximize recombinant protein expression in E. coli is to express the protein in a host bacteria with an impaired capacity to proteolytically cleave the recombinant protein (Gottesman, S., Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, California (1990) 119-128). Another strategy is to alter the nucleic acid sequence ofthe nucleic acid to be inserted into an expression vector so that the individual codons for each amino acid are those preferentially utilized in E. coli (Wada et al, (1992) Nucleic Acids Res. 20:21 1 1 -21 18). Such alteration of nucleic acid sequences of the invention can be carried out by standard DNA synthesis techniques. In another embodiment, the CARK expression vector is a yeast expression vector. Examples of vectors for expression in yeast S. cerivisae include pYepSecl (Baldari, et al, (1987) Embo J. 6:229-234), pMFa (Kurjan and Herskowitz. (1982) Celt 30:933-943), pJRY88 (Schultz et al, (1987) Gene 54: 1 13-123), pYES2 (Invitrogen Coφoration, San Diego, CA), and picZ (InVitrogen Coφ, San Diego, CA). Alternatively, CARK proteins can be expressed in insect cells using baculovirus expression vectors. Baculovirus vectors available for expression of proteins in cultured insect cells (e.g., Sf 9 cells) include the pAc series (Smith et al. (1983) Mol. Cell Bio 3:2156-2165) and the pVL series (Lucklow and Summers (1989) Virology 170:31-39). In yet another embodiment, a nucleic acid of the invention is expressed in mammalian cells using a mammalian expression vector. Examples of mammalian expression vectors include pCDM8 (Seed, B. (1987) Nature 329:840) and pMT2PC (Kaufman et al (1987) EMBO J. 6:187-195). When used in mammalian cells, the expression vector's control functions are often provided by viral regulatory elements. For example, commonly used promoters are derived from polyoma, Adenovirus 2, cytomegalovirus and Simian Virus 40. For other suitable expression systems for both prokaryotic and eukaryotic cells see chapters 16 and 17 of Sambrook, J.. Fritsh, E. F.. and Maniatis, T. Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring Harbor Laboratory. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989. In another embodiment, the recombinant mammalian expression vector is capable of directing expression ofthe nucleic acid preferentially in a particular cell type (e.g., tissue-specific regulatory elements are used to express the nucleic acid). Tissue- specific regulatory elements are known in the art. Non-limiting examples of suitable tissue-specific promoters include the albumin promoter (liver-specific; Pinkert et al. (1987) Genes Dev. 1 :268-277), lymphoid-specific promoters (Calame and Eaton (1988) Adv. Immunol. 43:235-275), in particular promoters of T cell receptors (Winoto and Baltimore (1989) EMBO J. 8:729-733) and immunoglobulins (Banerji et al. (1983) Cell 33:729-740; Queen and Baltimore (1983) Cell 33:741 -748), neuron-specific promoters (e.g., the neurofilament promoter; Byrne and Ruddle (1989) Proc. Natl. Acad. Sci. USA 86:5473-5477), pancreas-specific promoters (Edlund et al. (1985) Science 230:912-916), and mammary gland-specific promoters (e.g., milk whey promoter: U.S. Patent No. 4,873,316 and European Application Publication No. 264J66). Developmentally- regulated promoters are also encompassed, for example the murine hox promoters (Kessel and Gruss (1990) Science 249:374-379) and the -fetoprotein promoter (Campes and Tilghman (1989) Genes Dev. 3:537-546). The expression characteristics of an endogenous CARK gene within a cell line or microorganism may be modified by inserting a heterologous DNA regulatory element into the genome of a stable cell line or cloned microorganism such that the inserted regulatory element is operatively linked with the endogenous CARK gene. For example, an endogenous CARK gene which is normally "transcriptionally silent", i.e., a CARK gene which is normally not expressed, or is expressed only at very low levels in a cell line or microorganism, may be activated by inserting a regulatory element which is capable of promoting the expression of a normally expressed gene product in that cell line or microorganism. Alternatively, a transcriptionally silent, endogenous CARK gene may be activated by insertion of a promiscuous regulatory element that works across cell types. A heterologous regulatory element may be inserted into a stable cell line or cloned microorganism, such that it is operatively linked with an endogenous CARK gene, using techniques, such as targeted homologous recombination, which are well known to those of skill in the art, and described, e.g., in Chappel, U.S. Patent No. 5,272,071 ; PCT publication No. WO 91/06667, published May 16, 1991. The invention further provides a recombinant expression vector comprising a DNA molecule of the invention cloned into the expression vector in an antisense orientation. That is. the DNA molecule is operatively linked to a regulatory sequence in a manner which allows for expression (by transcription ofthe DNA molecule) of an RNA molecule which is antisense to CARK mRNA. Regulatory sequences operatively linked to a nucleic acid cloned in the antisense orientation can be chosen which direct the continuous expression of the antisense RNA molecule in a variety of cell types, for instance viral promoters and/or enhancers, or regulatory sequences can be chosen which direct constitutive, tissue specific or cell type specific expression of antisense RNA. The antisense expression vector can be in the form of a recombinant plasmid, phagemid or attenuated virus in which antisense nucleic acids are produced under the control of a high efficiency regulatory region, the activity of which can be determined by the cell type into which the vector is introduced. For a discussion ofthe regulation of gene expression using antisense genes see Weintraub, H. et al, Antisense RNA as a molecular tool for genetic analysis, Reviews - Trends in Genetics, Vol. 1 (1) 1986. Another aspect ofthe invention pertains to host cells into which a CARK nucleic acid molecule of the invention is introduced, e.g., a CARK nucleic acid molecule within a recombinant expression vector or a CARK nucleic acid molecule containing sequences which allow it to homologously recombine into a specific site of the host cell's genome. The terms "host cell" and "recombinant host cell" are used interchangeably herein. It is understood that such terms refer not only to the particular subject cell but to the progeny or potential progeny of such a cell. Because certain modifications may occur in succeeding generations due to either mutation or environmental influences, such progeny may not. in fact, be identical to the parent cell, but are still included within the scope of the term as used herein. A host cell can be any prokaryotic or eukaryotic cell. For example, a CARK protein can be expressed in bacterial cells such as E. coli, insect cells, yeast or mammalian cells (such as Chinese hamster ovary cells (CHO) or COS cells). Other suitable host cells are known to those skilled in the art. Vector DNA can be introduced into prokaryotic or eukaryotic cells via conventional transformation or transfection techniques. As used herein, the terms "transformation" and "transfection" are intended to refer to a variety of art-recognized techniques for introducing foreign nucleic acid (e.g., DNA) into a host cell, including calcium phosphate or calcium chloride co-precipitation, DΕAΕ-dextran-mediated transfection. lipofection, or electroporation. Suitable methods for transforming or transfecting host cells can be found in Sambrook, et al. (Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989), and other laboratory manuals. For stable transfection of mammalian cells, it is known that, depending upon the expression vector and transfection technique used, only a small fraction of cells may integrate the foreign DNA into their genome. In order to identify and select these integrants, a gene that encodes a selectable marker (e.g., resistance to antibiotics) is generally introduced into the host cells along with the gene of interest. Preferred selectable markers include those which confer resistance to drugs, such as G418, hygromycin and methotrexate. Nucleic acid encoding a selectable marker can be introduced into a host cell on the same vector as that encoding a CARK protein or can be introduced on a separate vector. Cells stably transfected with the introduced nucleic acid can be identified by drug selection (e.g., cells that have incoφorated the selectable marker gene will survive, while the other cells die). A host cell ofthe invention, such as a prokaryotic or eukaryotic host cell in culture, can be used to produce (i.e., express) a CARK protein. Accordingly, the invention further provides methods for producing a CARK protein using the host cells of the invention. In one embodiment, the method comprises culturing the host cell ofthe invention (into which a recombinant expression vector encoding a CARK protein has been introduced) in a suitable medium such that a CARK protein is produced. In another embodiment, the method further comprises isolating a CARK protein from the medium or the host cell. The host cells ofthe invention can also be used to produce non-human transgenic animals. For example, in one embodiment, a host cell ofthe invention is a fertilized oocyte or an embryonic stem cell into which CARK-coding sequences have been introduced. Such host cells can then be used to create non-human transgenic animals in which exogenous CARK sequences have been introduced into their genome or homologous recombinant animals in which endogenous CARK sequences have been altered. Such animals are useful for studying the function and/or activity of a CARK and for identifying and/or evaluating modulators of CARK activity. As used herein, a "transgenic animal" is a non-human animal, preferably a mammal, more preferably a rodent such as a rat or mouse, in which one or more of the cells ofthe animal includes a transgene. Other examples of transgenic animals include non-human primates, sheep, dogs, cows, goats, chickens, amphibians, and the like. A transgene is exogenous DNA which is integrated into the genome of a cell from which a transgenic animal develops and which remains in the genome ofthe mature animal, thereby directing the expression of an encoded gene product in one or more cell types or tissues of the transgenic animal. As used herein, a "homologous recombinant animal" is a non-human animal, preferably a mammal, more preferably a mouse, in which an endogenous CARK gene has been altered by homologous recombination between the endogenous gene and an exogenous DNA molecule introduced into a cell ofthe animal, e.g., an embryonic cell of the animal, prior to development ofthe animal. A transgenic animal ofthe invention can be created by introducing a CARK- encoding nucleic acid into the male pronuclei of a fertilized oocyte, e.g., by microinjection, retroviral infection, and allowing the oocyte to develop in a pseudopregnant female foster animal. The CARK cDNA sequence of SEQ ID NOJ can be introduced as a transgene into the genome of a non-human animal. Alternatively, a nonhuman homologue of a human CARK gene, such as a mouse or rat CARK gene (e.g., SEQ ID NO:7), can be used as a transgene. Alternatively, a CARK gene homologue, such as another CARK family member, can be isolated based on hybridization to the CARK cDNA sequences of SEQ ID NO: 1. 3, 7, or 9. or the DNA insert ofthe plasmid deposited with ATCC as Accession Number (described further in subsection I above) and used as a transgene. Intronic sequences and polyadenylation signals can also be included in the transgene to increase the efficiency of expression ofthe transgene. A tissue-specific regulatory sequence(s) can be operably linked to a CARK transgene to direct expression of a CARK protein to particular cells. Methods for generating transgenic animals via embryo manipulation and microinjection, particularly animals such as mice, have become conventional in the art and are described, for example, in U.S. Patent Nos. 4,736,866 and 4,870.009, both by Leder et al, U.S. Patent No. 4,873,191 by Wagner et al. and in Hogan, B.. Manipulating the Mouse Embryo, (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1986). Similar methods are used for production of other transgenic animals. A transgenic founder animal can be identified based upon the presence of a CARK transgene in its genome and/or expression of CARK mRNA in tissues or cells ofthe animals. A transgenic founder animal can then be used to breed additional animals carrying the transgene. Moreover, transgenic animals carrying a transgene encoding a CARK protein can further be bred to other transgenic animals carrying other transgenes. To create a homologous recombinant animal, a vector is prepared which contains at least a portion of a CARK gene into which a deletion, addition or substitution has been introduced to thereby alter, e.g., functionally disrupt, the CARK gene. The CARK gene can be a human gene (e.g.. the cDNA of SEQ ID NOJ). but more preferably, is a non-human homologue of a human CARK gene (e.g., SEQ ID NO:9, or a cDNA isolated by stringent hybridization with the nucleotide sequence of SEQ ID NOJ or 7). For example, a mouse CARK gene can be used to construct a homologous recombination nucleic acid molecule, e.g., a vector, suitable for altering an endogenous CARK gene in the mouse genome. In a preferred embodiment, the homologous recombination nucleic acid molecule is designed such that, upon homologous recombination, the endogenous CARK gene is functionally disrupted (i.e.. no longer encodes a functional protein: also referred to as a "knock out" vector). Alternatively, the homologous recombination nucleic acid molecule can be designed such that, upon homologous recombination, the endogenous CARK gene is mutated or otherwise altered but still encodes functional protein (e.g., the upstream regulatory region can be altered to thereby alter the expression ofthe endogenous CARK protein). In the homologous recombination nucleic acid molecule, the altered portion ofthe CARK gene is flanked at its 5' and 3' ends by additional nucleic acid sequence ofthe CARK gene to allow for homologous recombination to occur between the exogenous CARK gene carried by the homologous recombination nucleic acid molecule and an endogenous CARK gene in a cell, e.g., an embryonic stem cell. The additional flanking CARK nucleic acid sequence is of sufficient length for successful homologous recombination with the endogenous gene. Typically, several kilobases of flanking DNA (both at the 5' and 3' ends) are included in the homologous recombination nucleic acid molecule (see, e.g., Thomas, K.R. and Capecchi. M. R. (1987) Cell 51 :503 for a description of homologous recombination vectors). The homologous recombination nucleic acid molecule is introduced into a cell, e.g., an embryonic stem cell line (e.g., by electroporation) and cells in which the introduced CARK gene has homologously recombined with the endogenous CARK gene are selected (see e.g., Li, E. et al. (1992) Cell 69:915). The selected cells can then injected into a blastocyst of an animal (e.g., a mouse) to form aggregation chimeras (see e.g., Bradley, A. in Teratocarcinomas and Embryonic Stem Cells: A Practical Approach, E.J. Robertson, ed. (IRL, Oxford, 1987) pp. 1 13-152). A chimeric embryo can then be implanted into a suitable pseudopregnant female foster animal and the embryo brought to term. Progeny harboring the homologously recombined DNA in their germ cells can be used to breed animals in which all cells of the animal contain the homologously recombined DNA by germline transmission ofthe transgene. Methods for constructing homologous recombination nucleic acid molecules, e.g., vectors, or homologous recombinant animals are described further in Bradley, A. (1991) Current Opinion in Biotechnology 2:823-829 and in PCT International Publication Nos.: WO 90/1 1354 by Le Mouellec et al; WO 91/01 140 by Smithies et al; WO 92/0968 by Zijlstra et al; and WO 93/04169 by Berns et al. In another embodiment, transgenic non-human animals can be produced which contain selected systems which allow for regulated expression of the transgene. One example of such a system is the cre/loxP recombinase system of bacteriophage PI . For a description of the cre/loxP recombinase system, see, e.g., Lakso et al. (1992) Proc. Natl. Acad. Sci. USA 89:6232-6236. Another example of a recombinase system is the FLP recombinase system of Saccharomyces cerevisiae (O'Gorman et al. (1991) Science 251 :1351 -1355. If a cre/loxP recombinase system is used to regulate expression ofthe transgene. animals containing transgenes encoding both the Cre recombinase and a selected protein are required. Such animals can be provided through the construction of "double" transgenic animals, e.g., by mating two transgenic animals, one containing a transgene encoding a selected protein and the other containing a transgene encoding a recombinase. Clones ofthe non-human transgenic animals described herein can also be produced according to the methods described in Wilmut, I. et al. (1997) Nature 385:810- 813 and PCT International Publication Nos. WO 97/07668 and WO 97/07669. In brief, a cell, e.g.. a somatic cell, from the transgenic animal can be isolated and induced to exit the growth cycle and enter G 0 phase. The quiescent cell can then be fused, e.g., through the use of electrical pulses, to an enucleated oocyte from an animal of the same species from which the quiescent cell is isolated. The reconstructed oocyte is then cultured such that it develops to morula or blastocyte and then transferred to pseudopregnant female foster animal. The offspring borne of this female foster animal will be a clone of the animal from which the cell, e.g., the somatic cell, is isolated. IV. Pharmaceutical Compositions The CARK nucleic acid molecules, fragments of CARK proteins, and anti- CARK antibodies (also referred to herein as "active compounds") of the invention can be incoφorated into pharmaceutical compositions suitable for administration. Such compositions typically comprise the nucleic acid molecule, protein, or antibody and a pharmaceutically acceptable carrier. As used herein the language "pharmaceutically acceptable carrier" is intended to include any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active compound, use thereof in the compositions is contemplated. Supplementary active compounds can also be incoφorated into the compositions. A pharmaceutical composition of the invention is formulated to be compatible with its intended route of administration. Examples of routes of administration include parenteral, e.g., intravenous, intradermal, subcutaneous, oral (e.g., inhalation), transdermal (topical), transmucosal, and rectal administration. Solutions or suspensions used for parenteral, intradermal. or subcutaneous application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic. Pharmaceutical compositions suitable for injectable use include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersion. For intravenous administration, suitable carriers include physiological saline, bacteriostatic water, Cremophor EL™ (BASF, Parsippany, NJ) or phosphate buffered saline (PBS). In all cases, the composition must be sterile and should be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), and suitable mixtures thereof. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. Prevention ofthe action of microorganisms can be achieved by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, ascorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars, polyalcohols such as manitol. sorbitol, sodium chloride in the composition. Prolonged absoφtion ofthe injectable compositions can be brought about by including in the composition an agent which delays absoφtion. for example, aluminum monostearate and gelatin. Sterile injectable solutions can be prepared by incoφorating the active compound (e.g., a fragment of a CARK protein or an anti-CARK antibody) in the required amount in an appropriate solvent with one or a combination of ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incoφorating the active compound into a sterile vehicle which contains a basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and freeze-drying which yields a powder ofthe active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof. Oral compositions generally include an inert diluent or an edible carrier. They can be enclosed in gelatin capsules or compressed into tablets. For the puφose of oral therapeutic administration, the active compound can be incoφorated with excipients and used in the form of tablets, troches, or capsules, oral compositions can also be prepared using a fluid carrier for use as a mouthwash, wherein the compound in the fluid carrier is applied orally and swished and expectorated or swallowed. Pharmaceutically compatible binding agents, and/or adjuvant materials can be included as part of the composition. The tablets, pills, capsules, troches and the like can contain any ofthe following ingredients, or compounds of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose, a disintegrating agent such as alginic acid, Primogel, or corn starch; a lubricant such as magnesium stearate or Sterotes; a glidant such as colloidal silicon dioxide; a sweetening agent such as sucrose or saccharin: or a flavoring agent such as peppermint, methyl salicylate. or orange flavoring. For administration by inhalation, the compounds are delivered in the form of an aerosol spray from pressured container or dispenser which contains a suitable propellant, e.g., a gas such as carbon dioxide, or a nebulizer. Systemic administration can also be by transmucosal or transdermal means. For transmucosal or transdermal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art, and include, for example, for transmucosal administration, detergents, bile salts, and fusidic acid derivatives. Transmucosal administration can be accomplished through the use of nasal sprays or suppositories. For transdermal administration, the active compounds are formulated into ointments, salves, gels, or creams as generally known in the art. The compounds can also be prepared in the form of suppositories (e.g., with conventional suppository bases such as cocoa butter and other glycerides) or retention enemas for rectal delivery. In one embodiment, the active compounds are prepared with carriers that will protect the compound against rapid elimination from the body, such as a controlled release formulation, including implants and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides. polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. The materials can also be obtained commercially from Alza Coφoration and Nova Pharmaceuticals. Inc. Liposomal suspensions (including liposomes targeted to infected cells with monoclonal antibodies to viral antigens) can also be used as pharmaceutically acceptable carriers. These can be prepared according to methods known to those skilled in the art, for example, as described in U.S. Patent No. 4,522,81 1. It is especially advantageous to formulate oral or parenteral compositions in dosage unit form for ease of administration and uniformity of dosage. Dosage unit form as used herein refers to physically discrete units suited as unitary dosages for the subject to be treated: each unit containing a predetermined quantity of active compound calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. The specification for the dosage unit forms of the invention are dictated by and directly dependent on the unique characteristics of the active compound and the particular therapeutic effect to be achieved, and the limitations inherent in the art of compounding such an active compound for the treatment of individuals. Toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the LD50 (the dose lethal to 50%) ofthe population) and the ED50 (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index and it can be expressed as the ratio LD50/ED50. Compounds which exhibit large therapeutic indices are preferred. While compounds that exhibit toxic side effects may be used, care should be taken to design a delivery system that targets such compounds to the site of affected tissue in order to minimize potential damage to uninfected cells and, thereby, reduce side effects. The data obtained from the cell culture assays and animal studies can be used in formulating a range of dosage for use in humans. The dosage of such compounds lies preferably within a range of circulating concentrations that include the ED50 with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. For any compound used in the method of the invention, the therapeutically effective dose can be estimated initially from cell culture assays. A dose may be formulated in animal models to achieve a circulating plasma concentration range that includes the IC50 (i.e., the concentration of the test compound which achieves a half-maximal inhibition of symptoms) as determined in cell culture. Such information can be used to more accurately determine useful doses in humans. Levels in plasma may be measured, for example, by high performance liquid chromatography. As defined herein, a therapeutically effective amount of protein or polypeptide (i.e., an effective dosage) ranges from about 0.001 to 30 mg/kg body weight, preferably about 0.01 to 25 mg/kg body weight, more preferably about 0J to 20 mg/kg body weight, and even more preferably about 1 to 10 mg/kg, 2 to 9 mg/kg, 3 to 8 mg/kg. 4 to 7 mg/kg. or 5 to 6 mg/kg body weight. The skilled artisan will appreciate that certain factors may influence the dosage required to effectively treat a subject, including but not limited to the severity of the disease or disorder, previous treatments, the general health and/or age ofthe subject, and other diseases present. Moreover, treatment of a subject with a therapeutically effective amount of a protein, polypeptide, or antibody can include a single treatment or, preferably, can include a series of treatments. In a preferred example, a subject is treated with antibody, protein, or polypeptide in the range of between about 0J to 20 mg/kg body weight, one time per week for between about 1 to 10 weeks, preferably between 2 to 8 weeks, more preferably between about 3 to 7 weeks, and even more preferably for about 4. 5, or 6 weeks. It will also be appreciated that the effective dosage of antibody, protein, or polypeptide used for treatment may increase or decrease over the course of a particular treatment. Changes in dosage may result and become apparent from the results of diagnostic assays as described herein. The present invention encompasses agents which modulate expression or activity. An agent may. for example, be a small molecule. For example, such small molecules include, but are not limited to, peptides, peptidomimetics. amino acids, amino acid analogs, polynucleotides, polynucleotide analogs, nucleotides, nucleotide analogs, organic or inorganic compounds (i.e,. including heteroorganic and organometallic compounds) having a molecular weight less than about 10.000 grams per mole, organic or inorganic compounds having a molecular weight less than about 5,000 grams per mole, organic or inorganic compounds having a molecular weight less than about 1,000 grams per mole, organic or inorganic compounds having a molecular weight less than about 500 grams per mole, and salts, esters, and other pharmaceutically acceptable forms of such compounds. It is understood that appropriate doses of small molecule agents depends upon a number of factors within the ken of the ordinarily skilled physician, veterinarian, or researcher. The dose(s) ofthe small molecule will vary, for example, depending upon the identity, size, and condition ofthe subject or sample being treated, further depending upon the route by which the composition is to be administered, if applicable, and the effect which the practitioner desires the small molecule to have upon the nucleic acid or polypeptide of the invention. Exemplary doses include milligram or microgram amounts of the small molecule per kilogram of subject or sample weight (e.g., about 1 microgram per kilogram to about 500 milligrams per kilogram, about 100 micrograms per kilogram to about 5 milligrams per kilogram, or about 1 microgram per kilogram to about 50 micrograms per kilogram. It is furthermore understood that appropriate doses of a small molecule depend upon the potency of the small molecule with respect to the expression or activity to be modulated. Such appropriate doses may be determined using the assays described herein. When one or more of these small molecules is to be administered to an animal (e.g.. a human) in order to modulate expression or activity of a polypeptide or nucleic acid ofthe invention, a physician, veterinarian, or researcher may, for example, prescribe a relatively low dose at first, subsequently increasing the dose until an appropriate response is obtained. In addition, it is understood that the specific dose level for any particular animal subject will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, gender, and diet ofthe subject, the time of administration, the route of administration, the rate of excretion, any drug combination, and the degree of expression or activity to be modulated. Further, an antibody (or fragment thereof) may be conjugated to a therapeutic moiety such as a cytotoxin, a therapeutic agent or a radioactive metal ion. A cytotoxin or cytotoxic agent includes any agent that is detrimental to cells. Examples include taxol, cytochalasin B. gramicidin D, ethidium bromide, emetine, mitomycin, etoposide, tenoposide, vincristine, vinblastine, colchicin. doxorubicin, daunorubicin, dihydroxy anthracin dione, mitoxantrone, mithramycin, actinomycin D, 1 -dehydrotestosterone, glucocorticoids, procaine. tetracaine, lidocaine. propranolol, and puromycin and analogs or homologs thereof. Therapeutic agents include, but are not limited to, antimetabolites (e.g., methotrexate. 6-mercaptopurine, 6-thioguanine, cytarabine, 5-fluorouracil decarbazine), alkylating agents (e.g., mechlorethamine, thioepa chlorambucil, melphalan, carmustine (BSNU) and lomustine (CCNU), cyclothosphamide, busulfan, dibromomannitol. streptozotocin, mitomycin C, and cis-dichlorodiamine platinum (II) (DDP) cisplatin). anthracyclines (e.g., daunorubicin (formerly daunomycin) and doxorubicin), antibiotics (e g.. dactinomycin (formerly actinomycin), bleomycin, mithramycin, and anthramycin (AMC)), and anti-mitotic agents (e g., vincristine and vinblastine). The conjugates of the invention can be used for modifying a given biological response, the drug moiety is not to be construed as limited to classical chemical therapeutic agents. For example, the drug moiety may be a protein or polypeptide possessing a desired biological activity. Such proteins may include, for example, a toxin such as abrin, ricin A, pseudomonas exotoxin, or diphtheria toxin; a protein such as tumor necrosis factor, α-interferon, β-interferon, nerve growth factor, platelet derived growth factor, tissue plasminogen activator; or, biological response modifiers such as, for example, lymphokines, interleukin-1 ("IL-1 "), interleukin-2 ("IL-2"), interleukin-6 ("IL-6"), granulocyte macrophage colony stimulating factor ("GM-CSF"), granulocyte colony stimulating factor ("G-CSF"), or other growth factors. Techniques for conjugating such therapeutic moiety to antibodies are well known, see, e.g.. Arnon et al, "Monoclonal Antibodies For Immunotargeting Of Drugs In Cancer Therapy", in Monoclonal Antibodies And Cancer Therapy, Reisfeld et al. (eds.), pp. 243-56 (Alan R. Liss, Inc. 1985); Hellstrom et al, "Antibodies For Drug Delivery", in Controlled Drug Delivery (2nd Ed.), Robinson et al. (eds.), pp. 623-53 (Marcel Dekker. Inc. 1987); Thoφe, "Antibody Carriers Of Cytotoxic Agents In Cancer Therapy: A Review", in Monoclonal Antibodies '84: Biological And Clinical Applications. Pinchera et al. (eds.), pp. 475-506 (1985); "Analysis, Results, And Future Prospective Of The Therapeutic Use Of Radiolabeled Antibody In Cancer Therapy", in Monoclonal Antibodies For Cancer Detection And Therapy, Baldwin et al. (eds.), pp. 303-16 (Academic Press 1985), and Thoφe et al, "The Preparation And Cytotoxic Properties Of Antibody-Toxin Conjugates", Immunol. Rev., 62: 1 19-58 (1982). Alternatively, an antibody can be conjugated to a second antibody to form an antibody heteroconjugate as described by Segal in U.S. Patent No. 4,676,980. The nucleic acid molecules of the invention can be inserted into vectors and used as gene therapy vectors. Gene therapy vectors can be delivered to a subject by, for example, intravenous injection, local administration (see U.S. Patent 5,328,470) or by stereotactic injection (see e.g., Chen et al. (1994) Proc. Natl. Acad. Sci. USA 91 :3054- 3057). The pharmaceutical preparation of the gene therapy vector can include the gene therapy vector in an acceptable diluent, or can comprise a slow release matrix in which the gene delivery vehicle is imbedded. Alternatively, where the complete gene delivery vector can be produced intact from recombinant cells, e.g., retroviral vectors, the pharmaceutical preparation can include one or more cells which produce the gene delivery system. The pharmaceutical compositions can be included in a container, pack, or dispenser together with instructions for administration. V. Uses and Methods of the Invention The nucleic acid molecules, proteins, protein homologues, and antibodies described herein can be used in one or more ofthe following methods: a) screening assays; b) predictive medicine (e.g., diagnostic assays, prognostic assays, monitoring clinical trials, and pharmacogenetics); and c) methods of treatment (e.g., therapeutic and prophylactic). As described herein, a CARK protein ofthe invention has one or more of the following activities: 1) it regulates transmission of signals from cellular receptors, e.g., cardiac cell growth factor receptors; 2) it modulates the entry of cells, e.g.. cardiac precursor cells, into mitosis; 3) it modulates cellular differentiation; 4) it modulates cell death; and 5) it regulates cytoskeleton function, e.g., actin bundling, and, thus, can be used to, for example, 1) regulate transmission of signals from cellular receptors, e.g., cardiac cell growth factor receptors; 2) modulate the entry of cells, e.g., cardiac precursor cells, into mitosis; 3) modulate cellular differentiation; 4) modulate cell death; and 5) regulate cytoskeleton function, e.g., actin bundling. The isolated nucleic acid molecules ofthe invention can be used, for example, to express CARK protein (e.g., via a recombinant expression vector in a host cell in gene therapy applications), to detect CARK mRNA (e.g., in a biological sample) or a genetic alteration in a CARK gene, and to modulate CARK activity, as described further below. The CARK proteins can be used to treat disorders characterized by insufficient or excessive production of a CARK substrate or production of CARK inhibitors. In addition, the CARK proteins can be used to screen for naturally occurring CARK substrates, to screen for drugs or compounds which modulate CARK activity, as well as to treat disorders characterized by insufficient or excessive production of CARK protein or production of CARK protein forms which have decreased- aberrant or unwanted activity compared to CARK wild type protein (e.g.. cellular proliferation or differentiation associated disorders). Moreover, the anti-CARK antibodies ofthe invention can be used to detect and isolate CARK proteins, regulate the bioavailability of CARK proteins, and modulate CARK activity. A. Screening Assays: The invention provides a method (also referred to herein as a "screening assay") for identifying modulators, i.e., candidate or test compounds or agents (e.g., peptides, peptidomimetics, small molecules or other drugs) which bind to CARK proteins, have a stimulatory or inhibitory effect on, for example, CARK expression or CARK activity, or have a stimulatory or inhibitory effect on, for example, the expression or activity of CARK substrate. In one embodiment, the invention provides assays for screening candidate or test compounds which are substrates of a CARK protein or polypeptide or biologically active portion thereof. In another embodiment, the invention provides assays for screening candidate or test compounds which bind to or modulate the activity of a CARK protein or polypeptide or biologically active portion thereof. The test compounds ofthe present invention can be obtained using any ofthe numerous approaches in combinatorial library methods known in the art, including: biological libraries; spatially addressable parallel solid phase or solution phase libraries; synthetic library methods requiring deconvolution; the 'one-bead one-compound' library method; and synthetic library methods using affinity chromatography selection. The biological library approach is limited to peptide libraries, while the other four approaches are applicable to peptide, non-peptide oligomer or small molecule libraries of compounds (Lam, K.S. (1997) Anticancer Drug Des. 12: 145). Examples of methods for the synthesis of molecular libraries can be found in the art, for example in: DeWitt et al. (1993) Proc. Natl. Acad. Sci. U.S.A. 90:6909: Erb et al. (1994) Proc. Natl. Acad. Sci. USA 91 J 1422: Zuckermann et al. (1994). J. Med. Chem. 37:2678; Cho et al. (1993) Science 261 : 1303; Carrell et al. (1994) Angew. Chem. Int. Ed. Engl. 33:2059; Carell et al. (\994) Angew. Chem. Int. Ed. Engl. 33:2061 ; and in Gallop et al. (1994) ./. Med. Chem. 37:1233. Libraries of compounds may be presented in solution (e.g.. Houghten (1992) Biotechniques 13:412-421). or on beads (Lam (1991) Nature 354:82-84), chips (Fodor (1993) Nature 364:555-556). bacteria (Ladner U.S. Patent 5,223.409), spores (Ladner U.S. Patent '409). plasmids (Cull et al. (1992) Proc Natl Acad Sci USA 89: 1865-1869) or on phage (Scott and Smith (1990) Science 249:386-390); (Devlin (1990) Science 249:404-406); (Cwirla et al. (1990) Proc. Natl. Acad. Sci. 87:6378-6382); (Felici (1991) J. Mol. Biol. 222:301-310); (Ladner supra.). In one embodiment, an assay is a cell-based assay in which a cell which expresses a CARK protein or biologically active portion thereof is contacted with a test compound and the ability ofthe test compound to modulate CARK activity is determined. Determining the ability of the test compound to modulate CARK activity can be accomplished by monitoring, for example, intracellular calcium, IP3, or diacylglycerol concentration, phosphorylation profile of intracellular proteins, cell proliferation and/or migration, or the activity of a CARK-regulated transcription factor. The cell, for example, can be of mammalian origin, e.g., a cardiac cell. The ability ofthe test compound to modulate CARK binding to a substrate or to bind to CARK can also be determined. Determining the ability of the test compound to modulate CARK binding to a substrate can be accomplished, for example, by coupling the CARK substrate with a radioisotope or enzymatic label such that binding of the CARK substrate to CARK can be determined by detecting the labeled CARK substrate in a complex. Determining the ability of the test compound to bind CARK can be accomplished, for example, by coupling the compound with a radioisotope or enzymatic label such that binding ofthe compound to CARK can be determined by detecting the labeled CARK compound in a complex. For example, compounds (e.g., CARK substrates) can be labeled with 125^ ->5s. 14 or 3j-^ either directly or indirectly, and the radioisotope detected by direct counting of radioemmission or by scintillation counting. Alternatively, compounds can be enzymatically labeled with, for example, horseradish peroxidase. alkaline phosphatase. or luciferase, and the enzymatic label detected by determination of conversion of an appropriate substrate to product. It is also within the scope of this invention to determine the ability of a compound (e.g.. a CARK substrate) to interact with CARK without the labeling of any ofthe interactants. For example, a microphysiometer can be used to detect the interaction of a compound with CARK without the labeling of either the compound or the CARK. McConnell. H. M. et al. (\992) Science 257:1906-1912. As used herein, a "microphysiometer" (e.g., Cytosensor) is an analytical instrument that measures the rate at which a cell acidifies its environment using a light-addressable potentiometric sensor (LAPS). Changes in this acidification rate can be used as an indicator of the interaction between a compound and CARK. In another embodiment, an assay is a cell-based assay comprising contacting a cell expressing a CARK target molecule (e.g., a CARK substrate) with a test compound and determining the ability ofthe test compound to modulate (e.g. stimulate or inhibit) the activity of the CARK target molecule. Determining the ability of the test compound to modulate the activity of a CARK target molecule can be accomplished, for example, by determining the ability of the CARK protein to bind to or interact with the CARK target molecule. Determining the ability of the CARK protein or a biologically active fragment thereof, to bind to or interact with a CARK target molecule can be accomplished by one of the methods described above for determining direct binding. In a preferred embodiment, determining the ability of the CARK protein to bind to or interact with a CARK target molecule can be accomplished by determining the activity of the target molecule. For example, the activity of the target molecule can be determined by detecting induction of a cellular second messenger of the target (i.e., intracellular Ca + , diacylglycerol. IP3. and the like), detecting catalytic/enzymatic activity of the target an appropriate substrate, detecting the induction of a reporter gene (comprising a target- responsive regulatory element operatively linked to a nucleic acid encoding a detectable marker, e.g., luciferase), or detecting a target-regulated cellular response. In yet another embodiment, an assay of the present invention is a cell-free assay in which a CARK protein or biologically active portion thereof is contacted with a test compound and the ability of the test compound to bind to the CARK protein or biologically active portion thereof is determined. Preferred biologically active portions ofthe CARK proteins to be used in assays of the present invention include fragments which participate in interactions with non-CARK molecules, e.g., fragments with high surface probability scores (see, for example, Figure 2). Binding of the test compound to the CARK protein can be determined either directly or indirectly as described above. In a preferred embodiment, the assay includes contacting the CARK protein or biologically active portion thereof with a known compound which binds CARK to form an assay mixture, contacting the assay mixture with a test compound, and determining the ability ofthe test compound to interact with a CARK protein, wherein determining the ability of the test compound to interact with a CARK protein comprises determining the ability ofthe test compound to preferentially bind to CARK or biologically active portion thereof as compared to the known compound. In another embodiment, the assay is a cell-free assay in which a CARK protein or biologically active portion thereof is contacted with a test compound and the ability of the test compound to modulate (e.g., stimulate or inhibit) the activity ofthe CARK protein or biologically active portion thereof is determined. Determining the ability of the test compound to modulate the activity of a CARK protein can be accomplished, for example, by determining the ability ofthe CARK protein to bind to a CARK target molecule by one ofthe methods described above for determining direct binding. Determining the ability of the CARK protein to bind to a CARK target molecule can also be accomplished using a technology such as real-time Biomolecular Interaction Analysis (BIA). Sjolander, S. and Urbaniczky, C. (1991) Anal. Chem. 63:2338-2345 and Szabo et al. (1995) Curr. Opin. Struct. Biol. 5:699-705. As used herein, "BIA" is a technology for studying biospecific interactions in real time, without labeling any of the interactants (e.g., BIAcore). Changes in the optical phenomenon of surface plasmon resonance (SPR) can be used as an indication of real-time reactions between biological molecules. In an alternative embodiment, determining the ability ofthe test compound to modulate the activity of a CARK protein can be accomplished by determining the ability ofthe CARK protein to further modulate the activity of a downstream effector of a CARK target molecule. For example, the activity of the effector molecule on an appropriate target can be determined or the binding ofthe effector to an appropriate target can be determined as previously described. In yet another embodiment, the cell-free assay involves contacting a CARK protein or biologically active portion thereof with a known compound which binds the CARK protein to form an assay mixture, contacting the assay mixture with a test compound, and determining the ability of the test compound to interact with the CARK protein, wherein determining the ability ofthe test compound to interact with the CARK protein comprises determining the ability of the CARK protein to preferentially bind to or modulate the activity of a CARK target molecule. The cell-free assays ofthe present invention are amenable to use of both soluble and/or membrane-bound forms of isolated proteins (e.g., CARK proteins or biologically active portions thereof ). In the case of cell-free assays in which a membrane-bound form of an isolated protein is used it may be desirable to utilize a solubilizing agent such that the membrane-bound form ofthe isolated protein is maintained in solution. Examples of such solubilizing agents include non-ionic detergents such as n- octylglucoside, n-dodecylglucoside, n-dodecylmaltoside, octanoyl-N-methylglucamide, decanoyl-N-methylglucamide, Triton® X-100. Triton® X-l 14, Thesit®, Isotridecypoly(ethylene glycol ether) n , 3-[(3-cholamidopropyl)dimethylamminio]-l- propane sulfonate (CHAPS), 3-[(3-cholamidopropyl)dimethylamminio]-2-hydroxy-l- propane sulfonate (CHAPSO), or N-dodecyl=N,N-dimethyl-3-ammonio-l -propane sulfonate. In more than one embodiment ofthe above assay methods of the present invention, it may be desirable to immobilize either CARK or its target molecule to facilitate separation of complexed from uncomplexed forms of one or both of the proteins, as well as to accommodate automation of the assay. Binding of a test compound to a CARK protein, or interaction of a CARK protein with a target molecule in the presence and absence of a candidate compound, can be accomplished in any vessel suitable for containing the reactants. Examples of such vessels include microtitre plates, test tubes, and micro-centrifuge tubes. In one embodiment, a fusion protein can be provided which adds a domain that allows one or both of the proteins to be bound to a matrix. For example. glutathione-S-transferase/ CARK fusion proteins or glutathione-S- transferase/target fusion proteins can be adsorbed onto glutathione sepharose beads (Sigma Chemical. St. Louis. MO) or glutathione derivatized microtitre plates, which are then combined with the test compound or the test compound and either the non-adsorbed target protein or CARK protein, and the mixture incubated under conditions conducive to complex formation (e.g.. at physiological conditions for salt and pH). Following incubation, the beads or microtitre plate wells are washed to remove any unbound components, the matrix immobilized in the case of beads, complex determined either directly or indirectly, for example, as described above. Alternatively, the complexes can be dissociated from the matrix, and the level of CARK binding or activity determined using standard techniques. Other techniques for immobilizing proteins on matrices can also be used in the screening assays of the invention. For example, either a CARK protein or a CARK target molecule can be immobilized utilizing conjugation of biotin and streptavidin. Biotinylated CARK protein or target molecules can be prepared from biotin-NHS (N- hydroxy-succinimide) using techniques known in the art (e.g., biotinylation kit, Pierce Chemicals, Rockford. IL). and immobilized in the wells of streptavidin-coated 96 well plates (Pierce Chemical). Alternatively, antibodies reactive with CARK protein or target molecules but which do not interfere with binding ofthe CARK protein to its target molecule can be derivatized to the wells ofthe plate, and unbound target or CARK protein trapped in the wells by antibody conjugation. Methods for detecting such complexes, in addition to those described above for the GST-immobilized complexes, include immunodetection of complexes using antibodies reactive with the CARK protein or target molecule, as well as enzyme-linked assays which rely on detecting an enzymatic activity associated with the CARK protein or target molecule. In another embodiment, modulators of CARK expression are identified in a method wherein a cell is contacted with a candidate compound and the expression of CARK mRNA or protein in the cell is determined. The level of expression of CARK mRNA or protein in the presence of the candidate compound is compared to the level of expression of CARK mRNA or protein in the absence ofthe candidate compound. The candidate compound can then be identified as a modulator of CARK expression based on this comparison. For example, when expression of CARK mRNA or protein is greater (statistically significantly greater) in the presence ofthe candidate compound than in its absence, the candidate compound is identified as a stimulator of CARK mRNA or protein expression. Alternatively, when expression of CARK mRNA or protein is less (statistically significantly less) in the presence of the candidate compound than in its absence, the candidate compound is identified as an inhibitor of CARK mRNA or protein expression. In one embodiment, CARK mRNA or protein expression is monitored in a cell based model for a cardiovascular disorder, e.g., a model of cardiac myocyte hypertrophy (Kariya, K et αl. (1994) J. Biol. Chem., 269:3775-3782). The level of CARK mRNA or protein expression in the cells can be determined by methods described herein for detecting CARK mRNA or protein. In yet another aspect of the invention, the CARK proteins can be used as "bait proteins" in a two-hybrid assay or three-hybrid assay (see, e.g., U.S. Patent No. 5.283,317; Zervos et αl. (1993) Cell 72:223-232; Madura et αl. (1993) J. Biol. Chem. 268: 12046-12054; Bartel et αl. (1993) Biotechniques 14:920-924; Iwabuchi et αl. (1993) Oncogene 8:1693-1696; and Brent WO94/10300), to identify other proteins, which bind to or interact with CARK ("CARK-binding proteins" or "CARK-bp") and are involved in CARK activity. Such CARK-binding proteins are also likely to be involved in the propagation of signals by the CARK proteins or CARK targets as, for example, downstream elements of a CARK-mediated signaling pathway. Alternatively, such CARK-binding proteins are likely to be CARK inhibitors. The two-hybrid system is based on the modular nature of most transcription factors, which consist of separable DNA-binding and activation domains. Briefly, the assay utilizes two different DNA constructs. In one construct, the gene that codes for a CARK protein is fused to a gene encoding the DNA binding domain of a known transcription factor (e.g., GAL-4). In the other construct, a DNA sequence, from a library of DNA sequences, that encodes an unidentified protein ("prey" or "sample") is fused to a gene that codes for the activation domain of the known transcription factor. If the "bait" and the "prey" proteins are able to interact, in vivo, forming a CARK- dependent complex, the DNA-binding and activation domains ofthe transcription factor are brought into close proximity. This proximity allows transcription of a reporter gene (e.g., LacZ) which is operably linked to a transcriptional regulatory site responsive to the transcription factor. Expression ofthe reporter gene can be detected and cell colonies containing the functional transcription factor can be isolated and used to obtain the cloned gene which encodes the protein which interacts with the CARK protein. In another aspect, the invention pertains to a combination of two or more of the assays described herein. For example, a modulating agent can be identified using a cell- based or a cell free assay, and the ability of the agent to modulate the activity of a CARK protein can be confirmed in vivo, e.g., in an animal, such as an animal model for a cardiovascular disorder, e.g., a model of cardiac myocyte hypertrophy. This invention further pertains to novel agents identified by the above-described screening assays. Accordingly, it is within the scope of this invention to further use an agent identified as described herein in an appropriate animal model. For example, an agent identified as described herein (e.g., a CARK modulating agent, an antisense CARK nucleic acid molecule, a CARK-specific antibody, or a CARK-binding partner) can be used in an animal model to determine the efficacy, toxicity, or side effects of treatment with such an agent. Alternatively, an agent identified as described herein can be used in an animal model to determine the mechanism of action of such an agent. Furthermore, this invention pertains to uses of novel agents identified by the above- described screening assays for treatments as described herein. B. Detection Assays Portions or fragments of the cDNA sequences identified herein (and the corresponding complete gene sequences) can be used in numerous ways as polynucleotide reagents. For example, these sequences can be used to: (i) map their respective genes on a chromosome; and, thus, locate gene regions associated with genetic disease; (ii) identify an individual from a minute biological sample (tissue typing); and (iii) aid in forensic identification of a biological sample. These applications are described in the subsections below. 1. Chromosome Mapping Once the sequence (or a portion of the sequence) of a gene has been isolated, this sequence can be used to map the location ofthe gene on a chromosome. This process is called chromosome mapping. Accordingly, portions or fragments of the CARK nucleotide sequences, described herein, can be used to map the location of the CARK genes on a chromosome. The mapping ofthe CARK sequences to chromosomes is an important first step in correlating these sequences with genes associated with disease. The CARK gene has been mapped to human chromosome 1 , within the atrioventricular canal defects (AVCD) locus (Sheffield, VC et al. (1997) Human Molecular Genetics, 6: 1 17-121). Briefly, CARK genes can be mapped to chromosomes by preparing PCR primers (preferably 15-25 bp in length) from the CARK nucleotide sequences. Computer analysis of the CARK sequences can be used to predict primers that do not span more than one exon in the genomic DNA, thus complicating the amplification process. These primers can then be used for PCR screening of somatic cell hybrids containing individual human chromosomes. Only those hybrids containing the human gene corresponding to the CARK sequences will yield an amplified fragment. Somatic cell hybrids are prepared by fusing somatic cells from different mammals (e.g., human and mouse cells). As hybrids of human and mouse cells grow and divide, they gradually lose human chromosomes in random order, but retain the mouse chromosomes. By using media in which mouse cells cannot grow, because they lack a particular enzyme, but human cells can. the one human chromosome that contains the gene encoding the needed enzyme, will be retained. By using various media, panels of hybrid cell lines can be established. Each cell line in a panel contains either a single human chromosome or a small number of human chromosomes, and a full set of mouse chromosomes, allowing easy mapping of individual genes to specific human chromosomes. (D'Eustachio P. et al (1983) Science 220:919-924). Somatic cell hybrids containing only fragments of human chromosomes can also be produced by using human chromosomes with translocations and deletions. PCR mapping of somatic cell hybrids is a rapid procedure for assigning a particular sequence to a particular chromosome. Three or more sequences can be assigned per day using a single thermal cycler. Using the CARK nucleotide sequences to design oligonucleotide primers, sublocalization can be achieved with panels of fragments from specific chromosomes. Other mapping strategies which can similarly be used to map a CARK sequence to its chromosome include in situ hybridization (described in Fan. Y. et al (1990) Proc. Natl Acad. Sci. USA, 87:6223-27), pre- screening with labeled chromosomes, and pre-selection by hybridization to chromosome specific cDNA libraries. Fluorescence in situ hybridization (FISH) of a DNA sequence to a metaphase chromosomal spread can further be used to provide a precise chromosomal location in one step. Chromosome spreads can be made using cells whose division has been blocked in metaphase by a chemical such as colcemid that disrupts the mitotic spindle. The chromosomes can be treated briefly with trypsin, and then stained with Giemsa. A pattern of light and dark bands develops on each chromosome, so that the chromosomes can be identified individually. The FISH technique can be used with a DNA sequence as short as 500 or 600 bases. However, clones larger than 1,000 bases have a higher likelihood of binding to a unique chromosomal location with sufficient signal intensity for simple detection. Preferably 1,000 bases, and more preferably 2,000 bases will suffice to get good results at a reasonable amount of time. For a review of this technique, see Verma et al, Human Chromosomes: A Manual of Basic Techniques (Pergamon Press. New York 1988). Reagents for chromosome mapping can be used individually to mark a single chromosome or a single site on that chromosome, or panels of reagents can be used for marking multiple sites and/or multiple chromosomes. Reagents corresponding to noncoding regions of the genes actually are preferred for mapping puφoses. Coding sequences are more likely to be conserved within gene families, thus increasing the chance of cross hybridizations during chromosomal mapping. Once a sequence has been mapped to a precise chromosomal location, the physical position ofthe sequence on the chromosome can be correlated with genetic map data. (Such data are found, for example, in V. McKusick, Mendelian Inheritance in Man, available on-line through Johns Hopkins University Welch Medical Library). The relationship between a gene and a disease, mapped to the same chromosomal region, can then be identified through linkage analysis (co-inheritance of physically adjacent genes), described in. for example, Egeland, J. et al. (1987) Nature, 325:783-787. Moreover, differences in the DNA sequences between individuals affected and unaffected with a disease associated with the CARK gene, can be determined. If a mutation is observed in some or all ofthe affected individuals but not in any unaffected individuals, then the mutation is likely to be the causative agent ofthe particular disease. Comparison of affected and unaffected individuals generally involves first looking for structural alterations in the chromosomes, such as deletions or translocations that are visible from chromosome spreads or detectable using PCR based on that DNA sequence. Ultimately, complete sequencing of genes from several individuals can be performed to confirm the presence of a mutation and to distinguish mutations from polymoφhisms. 2. Tissue Typing The CARK sequences of the present invention can also be used to identify individuals from minute biological samples. The United States military, for example, is considering the use of restriction fragment length polymoφhism (RFLP) for identification of its personnel. In this technique, an individual's genomic DNA is digested with one or more restriction enzymes, and probed on a Southern blot to yield unique bands for identification. This method does not suffer from the current limitations of "Dog Tags" which can be lost, switched, or stolen, making positive identification difficult. The sequences ofthe present invention are useful as additional DNA markers for RFLP (described in U.S. Patent 5,272,057). Furthermore, the sequences of the present invention can be used to provide an alternative technique which determines the actual base-by-base DNA sequence of selected portions of an individual's genome. Thus, the CARK nucleotide sequences described herein can be used to prepare two PCR primers from the 5' and 3' ends ofthe sequences. These primers can then be used to amplify an individual's DNA and subsequently sequence it. Panels of corresponding DNA sequences from individuals, prepared in this manner, can provide unique individual identifications, as each individual will have a unique set of such DNA sequences due to allelic differences. The sequences of the present invention can be used to obtain such identification sequences from individuals and from tissue. The CARK nucleotide sequences of the invention uniquely represent portions of the human genome. Allelic variation occurs to some degree in the coding regions of these sequences, and to a greater degree in the noncoding regions. It is estimated that allelic variation between individual humans occurs with a frequency of about once per each 500 bases. Each of the sequences described herein can, to some degree, be used as a standard against which DNA from an individual can be compared for identification puφoses. Because greater numbers of polymoφhisms occur in the noncoding regions, fewer sequences are necessary to differentiate individuals. The noncoding sequences of SEQ ID NOJ or 7 can comfortably provide positive individual identification with a panel of perhaps 10 to 1,000 primers which each yield a noncoding amplified sequence of 100 bases. If predicted coding sequences, such as those in SEQ ID NOJ or 9 are used, a more appropriate number of primers for positive individual identification would be 500-2,000. If a panel of reagents from CARK nucleotide sequences described herein is used to generate a unique identification database for an individual, those same reagents can later be used to identify tissue from that individual. Using the unique identification database, positive identification of the individual, living or dead, can be made from extremely small tissue samples. 3. Use of Partial CARK Sequences in Forensic Biology DNA-based identification techniques can also be used in forensic biology. Forensic biology is a scientific field employing genetic typing of biological evidence found at a crime scene as a means for positively identifying, for example, a peφetrator of a crime. To make such an identification, PCR technology can be used to amplify DNA sequences taken from very small biological samples such as tissues, e.g., hair or skin, or body fluids, e.g., blood, saliva, or semen found at a crime scene. The amplified sequence can then be compared to a standard, thereby allowing identification ofthe origin of the biological sample. The sequences of the present invention can be used to provide polynucleotide reagents, e.g., PCR primers, targeted to specific loci in the human genome, which can enhance the reliability of DNA-based forensic identifications by. for example, providing another "identification marker" (i.e. another DNA sequence that is unique to a particular individual). As mentioned above, actual base sequence information can be used for identification as an accurate alternative to patterns formed by restriction enzyme generated fragments. Sequences targeted to noncoding regions of SEQ ID NO: 1 or 7 are particularly appropriate for this use as greater numbers of polymorphisms occur in the noncoding regions, making it easier to differentiate individuals using this technique. Examples of polynucleotide reagents include the CARK nucleotide sequences or portions thereof, e g.. fragments derived from the noncoding regions of SEQ ID NOJ or 7 having a length of at least 20 bases, preferably at least 30 bases. The CARK nucleotide sequences described herein can further be used to provide polynucleotide reagents, e.g., labeled or labelable probes which can be used in, for example, an in situ hybridization technique, to identify a specific tissue, e.g., brain tissue. This can be v er\ useful in cases where a forensic pathologist is presented with a tissue of unknown origin. Panels of such CARK probes can be used to identify tissue by species and/or by organ type. In a similar fashion, these reagents, e.g.. CARK primers or probes can be used to screen tissue culture for contamination (i.e. screen for the presence of a mixture of different types of cells in a culture). C. Predictive Medicine: The present invention also pertains to the field of predictive medicine in which diagnostic assays, prognostic assays, and monitoring clinical trials are used for prognostic (predictive) puφoses to thereby treat an individual prophylactically. Accordingly, one aspect ofthe present invention relates to diagnostic assays for determining CARK protein and/or nucleic acid expression as well as CARK activity, in the context of a biological sample (e.g., blood, serum, cells, tissue) to thereby determine whether an individual is afflicted with a disease or disorder, or is at risk of developing a disorder, associated with aberrant or unwanted CARK expression or activity. The invention also pro\ ides for prognostic (or predictive) assays for determining whether an individual is at risk of developing a disorder associated with CARK nucleic acid and/or protein expression or activity. For example, mutations in a CARK gene can be assayed in a biological sample. Such assays can be used for prognostic or predictive puφose to thereby prophylactically treat an individual prior to the onset of a disorder characterized by or associated with CARK nucleic acid and 'or protein expression or activity. In one embodiment, CARK nucleic acid and/or protein expression or activity can be used in diagnostic and prognostic assays to detect and/or treat a cardiovascular disorder, e.g.. cardiac hypertrophy, congestive heart failure, a congenital heart defect, e.g., an atrioventricular canal defect. Another aspect ofthe invention pertains to monitoring the influence of agents (e.g., drugs, compounds) on the expression or activity of CARK in clinical trials. These and other agents are described in further detail in the following sections. 1. Diagnostic Assays An exemplary method for detecting the presence or absence of CARK protein or nucleic acid in a biological sample involves obtaining a biological sample from a test subject and contacting the biological sample with a compound or an agent capable of detecting CARK protein or nucleic acid (e.g., mRNA, genomic DNA) that encodes CARK protein such that the presence of CARK protein or nucleic acid is detected in the biological sample. A preferred agent for detecting CARK mRNA or genomic DNA is a labeled nucleic acid probe capable of hybridizing to CARK mRNA or genomic DNA. The nucleic acid probe can be, for example, a full-length CARK nucleic acid, such as the nucleic acid of SEQ ID NOJ, 3, 7, or 9, or the DNA insert of the plasmid deposited with ATCC as Accession Number , or a portion thereof, such as an oligonucleotide of at least 15, 30, 50, 100, 250 or 500 nucleotides in length and sufficient to specifically hybridize under stringent conditions to CARK mRNA or genomic DNA. Other suitable probes for use in the diagnostic assays of the invention are described herein. A preferred agent for detecting CARK protein is an antibody capable of binding to CARK protein, preferably an antibody with a detectable label. Antibodies can be polyclonal, or more preferably, monoclonal. An intact antibody, or a fragment thereof (e.g., Fab or F(ab')2) can be used. The term "labeled", with regard to the probe or antibody, is intended to encompass direct labeling of the probe or antibody by coupling (i.e., physically linking) a detectable substance to the probe or antibody, as well as indirect labeling ofthe probe or antibody by reactivity with another reagent that is directly labeled. Examples of indirect labeling include detection of a primary antibody using a fluorescently labeled secondary antibody and end-labeling of a DNA probe with biotin such that it can be detected with fluorescently labeled streptavidin. The term "biological sample" is intended to include tissues, cells and biological fluids isolated from a subject, as well as tissues, cells and fluids present within a subject. That is, the detection method ofthe invention can be used to detect CARK mRNA, protein, or genomic DNA in a biological sample in vitro as well as in vivo. For example, in vitro techniques for detection of CARK mRNA include Northern hybridizations and in situ hybridizations. In vitro techniques for detection of CARK protein include enzyme linked immunosorbent assays (ELISAs), Western blots, immunoprecipitations and immunofluorescence. In vitro techniques for detection of CARK genomic DNA include Southern hybridizations. Furthermore, in vivo techniques for detection of CARK protein include introducing into a subject a labeled anti-CARK antibody. For example, the antibody can be labeled with a radioactive marker whose presence and location in a subject can be detected by standard imaging techniques. In one embodiment, the biological sample contains protein molecules from the test subject. Alternatively, the biological sample can contain mRNA molecules from the test subject or genomic DNA molecules from the test subject. A preferred biological sample is a serum sample isolated by conventional means from a subject. In another embodiment, the methods further involve obtaining a control biological sample from a control subject, contacting the control sample with a compound or agent capable of detecting CARK protein. mRNA, or genomic DNA, such that the presence of CARK protein, mRNA or genomic DNA is detected in the biological sample, and comparing the presence of CARK protein, mRNA or genomic DNA in the control sample with the presence of CARK protein, mRNA or genomic DNA in the test sample. The invention also encompasses kits for detecting the presence of CARK in a biological sample. For example, the kit can comprise a labeled compound or agent capable of detecting CARK protein or mRNA in a biological sample; means for determining the amount of CARK in the sample; and means for comparing the amount of CARK in the sample with a standard. The compound or agent can be packaged in a suitable container. The kit can further comprise instructions for using the kit to detect CARK protein or nucleic acid. 2. Prognostic Assays The diagnostic methods described herein can furthermore be utilized to identify subjects having or at risk of developing a disease or disorder associated with aberrant or unwanted CARK expression or activity. As used herein, the term "aberrant" includes a CARK expression or activity which deviates from the wild type CARK expression or activity. Aberrant expression or activity includes increased or decreased expression or activity, as well as expression or activity which does not follow the wild type developmental pattern of expression or the subcellular pattern of expression. For example, aberrant CARK expression or activity is intended to include the cases in which a mutation in the CARK gene causes the CARK gene to be under-expressed or over- expressed and situations in which such mutations result in a non-functional CARK protein or a protein which does not function in a wild-type fashion, e.g., a protein which does not interact with a CARK ligand or one which interacts with a non-CARK ligand. As used herein, the term "unwanted" includes an unwanted phenomenon involved in a biological response such as proliferation or differentiation. For example, the term unwanted includes a CARK expression or activity which is undesirable in a subject. The assays described herein, such as the preceding diagnostic assays or the following assays, can be utilized to identify a subject having or at risk of developing a disorder associated with a misregulation in CARK protein activity or nucleic acid expression, such as a cardiovascular disorder. Alternatively, the prognostic assays can be utilized to identify a subject having or at risk for developing a disorder associated with a misregulation in CARK protein activity or nucleic acid expression, such as a cardiovascular disorder. Thus, the present invention provides a method for identifying a disease or disorder associated with aberrant or unwanted CARK expression or activity in which a test sample is obtained from a subject and CARK protein or nucleic acid (e.g., mRNA or genomic DNA) is detected, wherein the presence of CARK protein or nucleic acid is diagnostic for a subject having or at risk of developing a disease or disorder associated with aberrant or unwanted CARK expression or activity. As used herein, a "test sample" refers to a biological sample obtained from a subject of interest. For example, a test sample can be a biological fluid (e.g.. serum), cell sample, or tissue. Furthermore. the prognostic assays described herein can be used to determine whether a subject can be administered an agent (e.g., an agonist, antagonist, peptidomimetic, protein, peptide, nucleic acid, small molecule, or other drug candidate) to treat a disease or disorder associated with aberrant or unwanted CARK expression or activity. For example, such methods can be used to determine whether a subject can be effectively treated with an agent for a cardiovascular disorder. Thus, the present invention provides methods for determining whether a subject can be effectively treated with an agent for a disorder associated with aberrant or unwanted CARK expression or activity in which a test sample is obtained and CARK protein or nucleic acid expression or activity is detected (e.g.. wherein the abundance of CARK protein or nucleic acid expression or activity is diagnostic for a subject that can be administered the agent to treat a disorder associated with aberrant or unwanted CARK expression or activity). The methods ofthe invention can also be used to detect genetic alterations in a CARK gene, thereby determining if a subject with the altered gene is at risk for a disorder characterized by misregulation in CARK protein activity or nucleic acid expression, such as a cardiovascular disorder. In preferred embodiments, the methods include detecting, in a sample of cells from the subject, the presence or absence of a genetic alteration characterized by at least one of an alteration affecting the integrity of a gene encoding a CARK-protein, or the mis-expression ofthe CARK gene. For example, such genetic alterations can be detected by ascertaining the existence of at least one of 1 ) a deletion of one or more nucleotides from a CARK gene; 2) an addition of one or more nucleotides to a CARK gene; 3) a substitution of one or more nucleotides of a CARK gene, 4) a chromosomal rearrangement of a CARK gene; 5) an alteration in the level of a messenger RNA transcript of a CARK gene, 6) aberrant modification of a CARK gene, such as ofthe methylation pattern ofthe genomic DNA, 7) the presence of a non- wild type splicing pattern of a messenger RNA transcript of a CARK gene, 8) a non-wild type level of a CARK-protein. 9) allelic loss of a CARK gene, and 10) inappropriate posttranslational modification of a CARK-protein. As described herein, there are a large number of assays known in the art which can be used for detecting alterations in a CARK gene. A preferred biological sample is a tissue or serum sample isolated by conventional means from a subject. In certain embodiments, detection ofthe alteration involves the use of a probe/primer in a polymerase chain reaction (PCR) (see, e.g., U.S. Patent Nos. 4,683,195 and 4,683,202), such as anchor PCR or RACE PCR, or, alternatively, in a ligation chain reaction (LCR) (see, e.g., Landegran et al (1988) Science 241 :1077-1080; and Nakazawa et al. ( 1994) Proc. Natl. Acad. Sci. USA 91 :360-364), the latter of which can be particularly useful for detecting point mutations in the CARK-gene (see Abravaya et al (1995) Nucleic Acids Res .23:675-682). This method can include the steps of collecting a sample of cells from a subject, isolating nucleic acid (e.g., genomic, mRNA or both) from the cells of the sample, contacting the nucleic acid sample with one or more primers which specifically hybridize to a CARK gene under conditions such that hybridization and amplification ofthe CARK-gene (if present) occurs, and detecting the presence or absence of an amplification product, or detecting the size of the amplification product and comparing the length to a control sample. It is anticipated that PCR and/or LCR may be desirable to use as a preliminary amplification step in conjunction with any ofthe techniques used for detecting mutations described herein. Alternative amplification methods include: self sustained sequence replication (Guatelli, J.C. et al, (1990) Proc. Natl. Acad. Sci. USA 87:1874-1878), transcriptional amplification system (Kwoh, D.Y. et al, (1989) Proc. Natl. Acad. Sci. USA 86:1 173- 1 177), Q-Beta Replicase (Lizardi, P.M. et al. (1988) Bio-Technology 6:1 197), or any other nucleic acid amplification method, followed by the detection of the amplified molecules using techniques well known to those of skill in the art. These detection schemes are especially useful for the detection of nucleic acid molecules if such molecules are present in very low numbers. In an alternative embodiment, mutations in a CARK gene from a sample cell can be identified by alterations in restriction enzyme cleavage patterns. For example, sample and control DNA is isolated, amplified (optionally), digested with one or more restriction endonucleases, and fragment length sizes are determined by gel electrophoresis and compared. Differences in fragment length sizes between sample and control DNA indicates mutations in the sample DNA. Moreover, the use of sequence specific ribozymes (see, for example, U.S. Patent No. 5,498,531) can be used to score for the presence of specific mutations by development or loss of a ribozyme cleavage site. In other embodiments, genetic mutations in CARK can be identified by hybridizing a sample and control nucleic acids, e.g., DNA or RNA, to high density arrays containing hundreds or thousands of oligonucleotides probes (Cronin, M.T. et al. (1996) Human Mutation 1: 244-255; Kozal, M.J. et al (1996) Nature Medicine 2: 753- 759). For example, genetic mutations in CARK can be identified in two dimensional arrays containing light-generated DNA probes as described in Cronin, M.T. et al. supra. Briefly, a first hybridization array of probes can be used to scan through long stretches of DNA in a sample and control to identify base changes between the sequences by making linear arrays of sequential overlapping probes. This step allows the identification of point mutations. This step is followed by a second hybridization array that allows the characterization of specific mutations by using smaller, specialized probe arrays complementary to all variants or mutations detected. Each mutation array is composed of parallel probe sets, one complementary to the wild-type gene and the other complementary to the mutant gene. In yet another embodiment, any of a variety of sequencing reactions known in the art can be used to directly sequence the CARK gene and detect mutations by comparing the sequence ofthe sample CARK with the corresponding wild-type (control) sequence. Examples of sequencing reactions include those based on techniques developed by Maxam and Gilbert ((1977) Proc. Natl. Acad. Sci. USA 74:560) or Sanger ((1977) Proc. Natl. Acad. Sci. USA 74:5463). It is also contemplated that any of a variety of automated sequencing procedures can be utilized when performing the diagnostic assays ((1995) Biotechniques 19:448), including sequencing by mass spectrometry (see, e.g., PCT International Publication No. WO 94/16101 ; Cohen et al. (1996) Adv. Chromatogr. 36:127-162; and Griffin et al. (1993) Appl. Biochem. Biotechnol. 38:147-159). Other methods for detecting mutations in the CARK gene include methods in which protection from cleavage agents is used to detect mismatched bases in RNA RNA or RNA/DNA heteroduplexes (Myers et al. (1985) Science 230:1242). In general, the art technique of "mismatch cleavage" starts by providing heteroduplexes of formed by hybridizing (labeled) RNA or DNA containing the wild-type CARK sequence with potentially mutant RNA or DNA obtained from a tissue sample. The double-stranded duplexes are treated with an agent which cleaves single-stranded regions ofthe duplex such as which will exist due to basepair mismatches between the control and sample strands. For instance, RNA/DNA duplexes can be treated with RNase and DNA/DNA hybrids treated with S 1 nuclease to enzymatically digesting the mismatched regions. In other embodiments, either DNA/DNA or RNA/DNA duplexes can be treated with hydroxylamine or osmium tetroxide and with piperidine in order to digest mismatched regions. After digestion of the mismatched regions, the resulting material is then separated by size on denaturing polyacrylamide gels to determine the site of mutation. See, for example, Cotton et al. (1988) Proc. Natl Acad Sci USA 85:4397; Saleeba et al. (1992) Methods Enzymol. 217:286-295. In a preferred embodiment, the control DNA or RNA can be labeled for detection. In still another embodiment, the mismatch cleavage reaction employs one or more proteins that recognize mismatched base pairs in double-stranded DNA (so called "DNA mismatch repair " enzymes) in defined systems for detecting and mapping point mutations in CARK cDNAs obtained from samples of cells. For example, the mutY enzyme of E. coli cleaves A at G/A mismatches and the thymidine DNA glycosylase from HeLa cells cleaves T at G/T mismatches (Hsu et al. (1994) Carcinogenesis 15:1657-1662). According to an exemplary embodiment, a probe based on a CARK sequence, e.g., a wild-type CARK sequence, is hybridized to a cDNA or other DNA product from a test cell(s). The duplex is treated with a DNA mismatch repair enzyme, and the cleavage products, if any, can be detected from electrophoresis protocols or the like. See, for example. U.S. Patent No. 5,459.039. In other embodiments, alterations in electrophoretic mobility will be used to identify mutations in CARK genes. For example, single strand conformation polymoφhism (SSCP) may be used to detect differences in electrophoretic mobility between mutant and wild type nucleic acids (Orita et al. (1989) Proc Natl. Acad. Sci USA: 86:2766, see also Cotton (1993) Mutat. Res. 285: 125-144; and Hayashi (1992) Genet. Anal. Tech. Appl. 9:73-79). Single-stranded DNA fragments of sample and control CARK nucleic acids will be denatured and allowed to renature. The secondary structure of single-stranded nucleic acids varies according to sequence, the resulting alteration in electrophoretic mobility enables the detection of even a single base change. The DNA fragments may be labeled or detected with labeled probes. The sensitivity of the assay may be enhanced by using RNA (rather than DNA), in which the secondary structure is more sensitive to a change in sequence. In a preferred embodiment, the subject method utilizes heteroduplex analysis to separate double stranded heteroduplex molecules on the basis of changes in electrophoretic mobility (Keen et al. (1991) Trends Genet 7:5). In yet another embodiment the movement of mutant or wild-type fragments in polyacrylamide gels containing a gradient of denaturant is assayed using denaturing gradient gel electrophoresis (DGGE) (Myers et al. (1985) Nature 313:495). When DGGE is used as the method of analysis, DNA will be modified to insure that it does not completely denature, for example by adding a GC clamp of approximately 40 bp of high-melting GC-rich DNA by PCR. In a further embodiment, a temperature gradient is used in place of a denaturing gradient to identify differences in the mobility of control and sample DNA (Rosenbaum and Reissner (1987) Biophys Chem 265:12753). Examples of other techniques for detecting point mutations include, but are not limited to. selective oligonucleotide hybridization, selective amplification, or selective primer extension. For example, oligonucleotide primers may be prepared in which the known mutation is placed centrally and then hybridized to target DNA under conditions which permit hybridization only if a perfect match is found (Saiki et al. (1986) Nature 324:163); Saiki et al. (1989) Proc. Natl Acad. Sci USA 86:6230). Such allele specific oligonucleotides are hybridized to PCR amplified target DNA or a number of different mutations when the oligonucleotides are attached to the hybridizing membrane and hybridized with labeled target DNA. Alternatively, allele specific amplification technology which depends on selective PCR amplification may be used in conjunction with the instant invention. Oligonucleotides used as primers for specific amplification may carry the mutation of interest in the center ofthe molecule (so that amplification depends on differential hybridization) (Gibbs et al. (1989) Nucleic Acids Res. 17:2437-2448) or at the extreme 3' end of one primer where, under appropriate conditions, mismatch can prevent, or reduce polymerase extension (Prossner (1993) Tibtech 11 :238). In addition it may be desirable to introduce a novel restriction site in the region of the mutation to create cleavage-based detection (Gasparini et al. (1992) Mol. Cell Probes 6: 1). It is anticipated that in certain embodiments amplification may also be performed using Taq ligase for amplification (Barany (1991) Proc. Natl. Acad. Sci USA 88: 189). In such cases, ligation will occur only if there is a perfect match at the 3' end ofthe 5' sequence making it possible to detect the presence of a known mutation at a specific site by looking for the presence or absence of amplification. The methods described herein may be performed, for example, by utilizing pre- packaged diagnostic kits comprising at least one probe nucleic acid or antibody reagent described herein, which may be conveniently used, e.g., in clinical settings to diagnose patients exhibiting symptoms or family history of a disease or illness involving a CARK gene. Furthermore, any cell type or tissue in which CARK is expressed may be utilized in the prognostic assays described herein. 3. Monitoring of Effects During Clinical Trials Monitoring the influence of agents (e.g., drugs) on the expression or activity of a CARK protein (e.g., the modulation signaling pathways associated with cellular growth and differentiation) can be applied not only in basic drug screening, but also in clinical trials. For example, the effectiveness of an agent determined by a screening assay as described herein to increase CARK gene expression, protein levels, or upregulate CARK activity, can be monitored in clinical trials of subjects exhibiting decreased CARK gene expression, protein levels, or downregulated CARK activity. Alternatively, the effectiveness of an agent determined by a screening assay to decrease CARK gene expression, protein levels, or downregulate CARK activity, can be monitored in clinical trials of subjects exhibiting increased CARK gene expression, protein levels, or upregulated CARK activity. In such clinical trials, the expression or activity of a CARK gene, and preferably, other genes that have been implicated in, for example, a CARK- associated disorder can be used as a "read out" or markers of the phenotype of a particular cell. For example, and not by way of limitation, genes, including CARK. that are modulated in cells by treatment with an agent (e.g., compound, drug or small molecule) which modulates CARK activity (e.g., identified in a screening assay as described herein) can be identified. Thus, to study the effect of agents on CARK-associated disorders (e.g., disorders characterized by deregulated cellular growth or differentiation), for example, in a clinical trial, cells can be isolated and RNA prepared and analyzed for the levels of expression of CARK and other genes implicated in the CARK-associated disorder, respectively. The levels of gene expression (e.g., a gene expression pattern) can be quantified by northern blot analysis or RT-PCR, as described herein, or alternatively by measuring the amount of protein produced, by one of the methods as described herein, or by measuring the levels of activity of CARK or other genes. In this way, the gene expression pattern can serve as a marker, indicative of the physiological response ofthe cells to the agent. Accordingly, this response state may be determined before, and at various points during treatment ofthe individual with the agent. In a preferred embodiment, the present invention provides a method for monitoring the effectiveness of treatment of a subject with an agent (e.g., an agonist, antagonist, peptidomimetic, protein, peptide, nucleic acid, small molecule, or other drug candidate identified by the screening assays described herein) including the steps of (i) obtaining a pre-administration sample from a subject prior to administration ofthe agent; (ii) detecting the level of expression of a CARK protein, mRNA, or genomic DNA in the preadministration sample; (iii) obtaining one or more post-administration samples from the subject; (iv) detecting the level of expression or activity ofthe CARK protein, mRNA, or genomic DNA in the post-administration samples; (v) comparing the level of expression or activity ofthe CARK protein, mRNA, or genomic DNA in the pre-administration sample with the CARK protein, mRNA, or genomic DNA in the post administration sample or samples; and (vi) altering the administration of the agent to the subject accordingly. For example, increased administration ofthe agent may be desirable to increase the expression or activity of CARK to higher levels than detected, i.e., to increase the effectiveness ofthe agent. Alternatively, decreased administration of the agent may be desirable to decrease expression or activity of CARK to lower levels than detected, i.e. to decrease the effectiveness of the agent. According to such an embodiment, CARK expression or activity may be used as an indicator ofthe effectiveness of an agent, even in the absence of an observable phenotypic response. D. Methods of Treatment: The present invention provides for both prophylactic and therapeutic methods of treating a subject at risk of (or susceptible to) a disorder or having a disorder associated with aberrant or unwanted CARK expression or activity. With regards to both prophylactic and therapeutic methods of treatment, such treatments may be specifically tailored or modified, based on knowledge obtained from the field of pharmacogenomics. "Pharmacogenomics". as used herein, refers to the application of genomics technologies such as gene sequencing, statistical genetics, and gene expression analysis to drugs in clinical development and on the market. More specifically, the term refers the study of how a patient's genes determine his or her response to a drug (e.g., a patient's "drug response phenotype", or "drug response genotype".) Thus, another aspect ofthe invention provides methods for tailoring an individual's prophylactic or therapeutic treatment with either the CARK molecules of the present invention or CARK modulators according to that individual's drug response genotype. Pharmacogenomics allows a clinician or physician to target prophylactic or therapeutic treatments to patients who will most benefit from the treatment and to avoid treatment of patients who will experience toxic drug-related side effects. 1. Prophylactic Methods In one aspect, the invention provides a method for preventing in a subject, a disease or condition associated with an aberrant or unwanted CARK expression or activity, by administering to the subject a CARK or an agent which modulates CARK expression or at least one CARK activity. Subjects at risk for a disease which is caused or contributed to by aberrant or unwanted CARK expression or activity can be identified by, for example, any or a combination of diagnostic or prognostic assays as described herein. Administration of a prophylactic agent can occur prior to the manifestation of symptoms characteristic of the CARK aberrancy, such that a disease or disorder is prevented or, alternatively, delayed in its progression. Depending on the type of CARK aberrancy, for example, a CARK, CARK agonist or CARK antagonist agent can be used for treating the subject. The appropriate agent can be determined based on screening assays described herein. 2. Therapeutic Methods Another aspect of the invention pertains to methods of modulating CARK expression or activity for therapeutic puφoses. Accordingly, in an exemplary embodiment, the modulatory method of the invention involves contacting a cell with a CARK or agent that modulates one or more ofthe activities of CARK protein activity associated with the cell. An agent that modulates CARK protein activity can be an agent as described herein, such as a nucleic acid or a protein, a naturally-occurring target molecule of a CARK protein (e.g., a CARK substrate), a CARK antibody, a CARK agonist or antagonist, a peptidomimetic of a CARK agonist or antagonist, or other small molecule. In one embodiment, the agent stimulates one or more CARK activities. Examples of such stimulatory agents include active CARK protein and a nucleic acid molecule encoding CARK that has been introduced into the cell. In another embodiment, the agent inhibits one or more CARK activities. Examples of such inhibitory agents include antisense CARK nucleic acid molecules, anti-CARK antibodies, and CARK inhibitors. These modulatory methods can be performed in vitro (e.g., by culturing the cell with the agent) or, alternatively, in vivo (e.g., by administering the agent to a subject). As such, the present invention provides methods of treating an individual afflicted with a disease or disorder characterized by aberrant or unwanted expression or activity of a CARK protein or nucleic acid molecule. In one embodiment, the method involves administering an agent (e.g., an agent identified by a screening assay described herein), or combination of agents that modulates (e.g., upregulates or downregulates) CARK expression or activity. In another embodiment, the method involves administering a CARK protein or nucleic acid molecule as therapy to compensate for reduced, aberrant, or unwanted CARK expression or activity. For example, stimulation of CARK activity is desirable in situations in which CARK is abnormally downregulated and/or in which increased CARK activity is likely to have a beneficial effect. Likewise, inhibition of CARK activity is desirable in situations in which CARK is abnormally upregulated and/or in which decreased CARK activity is likely to have a beneficial effect. 3. Pharmacogenomics The CARK molecules of the present invention, as well as agents, or modulators which have a stimulatory or inhibitory effect on CARK activity (e.g., CARK gene expression) as identified by a screening assay described herein can be administered to individuals to treat (prophylactically or therapeutically) CARK-associated disorders (e.g., cardiovascular disorders) associated with aberrant or unwanted CARK activity. In conjunction with such treatment, pharmacogenomics (i.e., the study ofthe relationship between an individual's genotype and that individual's response to a foreign compound or drug) may be considered. Differences in metabolism of therapeutics can lead to severe toxicity or therapeutic failure by altering the relation between dose and blood concentration of the pharmacologically active drug. Thus, a physician or clinician may consider applying knowledge obtained in relevant pharmacogenomics studies in determining whether to administer a CARK molecule or CARK modulator as well as tailoring the dosage and/or therapeutic regimen of treatment with a CARK molecule or CARK modulator. Pharmacogenomics deals with clinically significant hereditary variations in the response to drugs due to altered drug disposition and abnormal action in affected persons. See, for example, Eichelbaum, M. et al. (1996) Clin. Exp. Pharmacol. Physiol. 23(10-11) :983-985 and Linder, M.W. et al. (1997) Clin. Chem. 43(2):254-266. In general, two types of pharmacogenetic conditions can be differentiated. Genetic conditions transmitted as a single factor altering the way drugs act on the body (altered drug action) or genetic conditions transmitted as single factors altering the way the body acts on drugs (altered drug metabolism). These pharmacogenetic conditions can occur either as rare genetic defects or as naturally-occurring polymorphisms. For example, glucose-6-phosphate dehydrogenase deficiency (G6PD) is a common inherited enzymopathy in which the main clinical complication is haemolysis after ingestion of oxidant drugs (anti-malarials, sulfonamides, analgesics, nitro furans) and consumption of fava beans. One pharmacogenomics approach to identifying genes that predict drug response, known as "a genome-wide association", relies primarily on a high-resolution map of the human genome consisting of already known gene-related markers (e.g., a "bi- allelic" gene marker map which consists of 60,000-100,000 polymoφhic or variable sites on the human genome, each of which has two variants.) Such a high-resolution genetic map can be compared to a map ofthe genome of each of a statistically significant number of patients taking part in a Phase II/III drug trial to identify markers associated with a particular observed drug response or side effect. Alternatively, such a high resolution map can be generated from a combination of some ten-million known single nucleotide polymoφhisms (SNPs) in the human genome. As used herein, a "SNP" is a common alteration that occurs in a single nucleotide base in a stretch of DNA. For example, a SNP may occur once per every 1000 bases of DNA. A SNP may be involved in a disease process, however, the vast majority may not be disease- associated. Given a genetic map based on the occurrence of such SNPs. individuals can be grouped into genetic categories depending on a particular pattern of SNPs in their individual genome. In such a manner, treatment regimens can be tailored to groups of genetically similar individuals, taking into account traits that may be common among such genetically similar individuals. Alternatively, a method termed the "candidate gene approach", can be utilized to identify genes that predict drug response. According to this method, if a gene that encodes a drugs target is known (e.g., a CARK protein ofthe present invention), all common variants of that gene can be fairly easily identified in the population and it can be determined if having one version ofthe gene versus another is associated with a particular drug response. As an illustrative embodiment, the activity of drug metabolizing enzymes is a major determinant of both the intensity and duration of drug action. The discovery of genetic polymoφhisms of drug metabolizing enzymes (e.g., N-acetyltransferase 2 (NAT 2) and cytochrome P450 enzymes CYP2D6 and CYP2C19) has provided an explanation as to why some patients do not obtain the expected drug effects or show exaggerated drug response and serious toxicity after taking the standard and safe dose of a drug. These polymoφhisms are expressed in two phenotypes in the population, the extensive metabolizer (EM) and poor metabolizer (PM). The prevalence of PM is different among different populations. For example, the gene coding for CYP2D6 is highly polymoφhic and several mutations have been identified in PM, which all lead to the absence of functional CYP2D6. Poor metabolizers of CYP2D6 and CYP2C19 quite frequently experience exaggerated drug response and side effects when they receive standard doses. If a metabolite is the active therapeutic moiety, PM show no therapeutic response, as demonstrated for the analgesic effect of codeine mediated by its CYP2D6-formed metabolite moφhine. The other extreme are the so called ultra-rapid metabolizers who do not respond to standard doses. Recently, the molecular basis of ultra-rapid metabolism has been identified to be due to CYP2D6 gene amplification. Alternatively, a method termed the "gene expression profiling", can be utilized to identify genes that predict drug response. For example, the gene expression of an animal dosed with a drug (e.g., a CARK molecule or CARK modulator of the present invention) can give an indication whether gene pathways related to toxicity have been turned on. Information generated from more than one of the above pharmacogenomics approaches can be used to determine appropriate dosage and treatment regimens for prophylactic or therapeutic treatment an individual. This knowledge, when applied to dosing or drug selection, can avoid adverse reactions or therapeutic failure and thus enhance therapeutic or prophylactic efficiency when treating a subject with a CARK molecule or CARK modulator, such as a modulator identified by one ofthe exemplary screening assays described herein. This invention is further illustrated by the following examples which should not be construed as limiting. The contents of all references, patents and published patent applications cited throughout this application are incoφorated herein by reference. EXAMPLES EXAMPLE 1 : Identification and Characterization of Human and Rat CARK cDNAs In this example, the identification and characterization ofthe genes encoding human CARK (clone fchrf013f03) and rat CARK (clone ??) is described. Isolation of the human and rat CARK cDNAs The invention is based, at least in part, on the discovery ofthe human and rat genes encoding CARK. The human CARK gene was isolated from a cDNA library which was prepared from tissue obtained from subjects suffering from congestive heart failure of ischemic and idiopathic origin. Briefly, a cardiac tissue sample was obtained from a biopsy of four patients suffering from congestive heart failure. mRNA was isolated from the cardiac tissue and a cDNA library was prepared therefrom using art known methods (described in, for example. Molecuktr Cloning A Laboratory Manual, 2nd Ed., ed. by Sambrook, Fritsch and Maniatis (Cold Spring Harbor Laboratory Press: 1989). Positive clones were isolated from these libraries using appropriate primers. The sequence of the positive clone was determined and found to contain an open reading frame. The nucleotide sequence encoding the human CARK protein comprises about 3025 nucleic acids, and has the nucleic acid sequence shown in Figure 1 and set forth as SEQ ID NOJ . The protein encoded by this nucleic acid comprises about 835 amino acids, and has the amino acid sequence shown in Figure 1 and set forth as SEQ ID NO:2. A clone containing the rat CARK cDNA was also identified. The nucleotide sequence encoding the rat CARK protein comprises about 3026 nucleic acids, and has the nucleic acid sequence shown in Figure 5 and set forth as SEQ ID NO:7. The protein encoded by this nucleic acid comprises about 835 amino acids, and has the amino acid sequence shown in Figure 5 and set forth as SEQ ID NO:8. Analysis of human CARK A BLASTP 1.4 search (Altschul et al. (1990) ./. Mol. Biol. 215:403) of the protein sequence of human CARK revealed that CARK is similar to the C elegans protein containing similarity to ankyrin repeats and protein kinase motifs (Accession No. AF024491). This protein is approximately 42% identical (over CARK amino acids 126-370), 60% identical (over CARK amino acids 421-548), 65% identical (over CARK amino acids 582-686), 32% identical (over CARK amino acids 60-222). 75% identical (over CARK amino acids 381-404), 36% identical (over CARK amino acids 122-167), 48%o identical (over CARK amino acids 10-36), 38% identical (over CARK amino acids 91-126), 52% identical (over CARK amino acids 556-678), 24% identical (over CARK amino acids 315-368). 25% identical (over CARK amino acids 74-161). and 29%o identical (over CARK amino acids 219-259) at the amino acid level. A BLASTN 1.4.9 search (Altschul et al. (1990) . Mol. Biol. 215:403) ofthe nucleotide sequence of human CARK revealed that CARK is similar to Homo sapiens cDNA clone 1320937 (Accession No. AA758546). The CARK nucleic acid molecule is 100%o identical to Homo sapiens cDNA clone 1320937 (Accession No. AA758546) over nucleotides 2544 to 3010. Analysis of primary and secondary protein structures, as shown in Figure 2. was performed as follows: alpha, beta turn and coil regions. Garnier-Robson algorithm (Gamier et al (1978) J Mol Biol 120:97); alpha, beta, and turn regions. Chou-Fasman algorithm (Chou and Fasman (1978) Adv in Enzymol Mol 47:45-148); hydrophilicity and hydrophobicity plots. Kyte-Doolittle algorithm (Kyte and Doolittle (1982) J Mol Biol 157:105-132); alpha amphipathic and beta amphipathic regions, Eisenberg algorithm (Eisenberg et al (1982) Nature 299:31 \ -314); flexible regions, Karplus-Schulz algorithm (Kaφlus and Schulz ( 1985) Naturwissens-Chafen 72:212-213); antigenic index. Jameson- Wolf algorithm (Jameson and Wolf (1988) CABIOS 4: \2\-\36): surface probability plot. Emini algorithm (Emini et al. (1985) J Virol 55:836-839). The CARK protein was aligned with the A. Thaliana kinase 2 (Accession No.Z97337). A. Thaliana kinase 3 (Accession No. AC0031 13). Arabidopsis thaliana (Accession No. AL031 135), C. elegans kinase (Accession No. AF024491), D. discoideum protein tyrosine kinase (Accession No. A35670), D. discoideum protein tyrosine kinase (Accession No. U01064). H. sapiens serine/threonine kinase (Accession No. Z48615), human rafl (Accession No. W13107), human Rafl kinase (Accession No. R98215), and soybean kinase (Accession No. M67449) using the Clustal method with a PAM250 residue weight table. This alignment is shown in Figure 3. Analvsis of rat CARK A BLASTP 1.4 search (Altschul et al. (1990) J. Mol. Biol. 215:403) ofthe protein sequence of rat CARK revealed that CARK is similar to the Homo sapiens putative protein tyrosine kinase (Accession No. AFl 16826). Rat CARK is approximately 91% identical to the Homo sapiens putative protein tyrosine kinase (Accession No. AFl 16826) over amino acid residues 1-835. Rat CARK is also similar to the C. elegans protein containing similarity to ankyrin repeats and protein kinase motifs (Accession No. AF024491). Rat CARK is approximately 41% identical to the C. elegans protein containing similarity to ankyrin repeats and protein kinase motifs over amino acid residues 39-720, and 39% identical over amino acid residues 10-370. A BLASTN 1.4.9 search (Altschul et al. (1990) J. Mol. Biol. 215:403) of the nucleotide sequence of rat CARK revealed that CARK is similar to the Homo sapiens clone HH498 putative protein-tyrosine kinase mRNA (Accession No. AFl 16826). The rat CARK nucleic acid molecule is 81%o identical to the Homo sapiens clone HH498 putative protein-tyrosine kinase mRNA (Accession No. AFl 16826) over nucleotides 27 to 2987. and 63% identical over nucleotides 2752 to 2999. The rat CARK nucleic acid sequence was globally aligned with the human CARK nucleic acid sequence using the GAP program in the GCG software package, using a nwsgapdna matrix a gap weight of 12 and a length weight of 4. The results showed a 82.2% identity between the two sequences (see Figure 7). The rat CARK protein sequence was globally aligned with the human CARK protein sequence using the GAP program in the GCG software package, using a Blosum 62 matrix and a gap weight of 12 and a length weight of 4. The results showed a 91.4% identity between the two sequences (see Figure 8). Tissue Distribution of CARK mRNA This Example describes the tissue distribution of CARK mRNA, as determined by Northern blot hybridization. Northern blot hybridization with the RNA sample was performed under standard conditions and washed under stringent conditions, i.e.. 0.2 X SSC at 65°C. A DNA probe corresponding to human CARK (clone fchrft)13fO3) was used. The DNA was radioactively labeled with J P-dCTP using the Prime-It kit (Stratagene. La Jolla, CA) according to the instructions ofthe supplier. Filters containing human mRNA, human muscle mRNA, and rat mRNA (MultiTissue Northern blots #7760-1 , #7765-1 , and #7764-1 , respectively, from Clontech, Palo Alto, CA) were probed in ExpressHyb hybridization solution (Clontech) and washed at high stringency conditions according to the manufacturer's recommendations. On the human mRNA blot which contained mRNA from heart, brain, placenta, lung, liver, skeletal muscle, kidney, and pancreas, CARK message was strongly detected in heart and faintly in skeletal muscle. On the human muscle mRNA blot which contained mRNA from skeletal muscle, uterus, colon, small intestine, bladder, heart, stomach, and prostate, CARK message was strongly detected in the heart. On the rat mRNA blot which contained mRNA from heart, brain, spleen, lung, liver, skeletal muscle, kidney and testis. CARK message was strongly detected in the heart. Chromosome Mapping of the CARK Gene The CARK gene was found to map to human chromosome 1 , within the atrioventricular canal defects (AVCD) locus (Sheffield, VC et al (1997) Human Molecular Genetics, 6: 1 17-121). Therefore, the CARK gene is a candidate for a congenital heart defect susceptibility gene, e.g., a septal defect, a endocardial cushion defect, a vessel defect, or a valvular defect. EXAMPLE 2: Regulation of CARK Expression in Cardiac Myocytes This Example describes the regulation of CARK expression in a cell culture model of cardiac hypertrophy. Briefly, primary cultures of neonatal cardiac myocytes were incubated for up to 24 hours in serum free minimal essential medium (MEM) supplemented with transferrin (10 μg/ml), insulin (10 μg/ml), and bovine serum albumin (1 mg/ml) (Kariya, K et al. (1994) . Biol. Chem., 269:3775-3782). The αl-adrenergic agonist L-phenylephrine (20 μM) was added during the incubation period to induce cardiac myocyte hypertrophy. Alternatively, cells were treated with angiotensin II (All, 10 μM), insulin-like growth factor (IGF, 1 ng/ml), transforming growth factor-β (TGF-β, 1 ng/ml), or tumor necrosis factor-α (TNF-α. 1 ng/ml). RNA was harvested for Northern blot analysis. Stimulation of cardiac myocytes with the hypertrophic agonist phenylephrine resulted in the down-regulation of CARK mRNA in a time dependent fashion, with CARK mRNA reaching almost undetectable levels between 12 and 24 hours following treatment. The expression of atrial naturetic factor (ANF) and sarcoplasmic reticulum- Ca(2+)-ATPase (SERCA2) which are known to be regulated during myocyte hypertrophy was also assessed. ANF mRNA was induced and SERCA2 mRNA was down-regulated following phenylephrine treatment. The gene encoding the CHO-B ribosomal protein was used as a control gene which is not regulated during hypertrophy. The effect of phenylephrine on CARK regulation is specific, as treatment with All, IGF, TGF-β and TNF-α did not have any effect on CARK expression. These growth factors also did not induce a state of hypertrophy, as they did not induce ANF expression. The CARK gene is specifically downregulated in response to the αl-adrenergic agonist L-phenylephrine in a cell culture model of cardiac hypertrophy, and may thus play a role in cellular signal transduction pathways that regulate cardiac myocyte growth and differentiation. The regulation of the CARK gene during cardiac myocyte hypertrophy may be useful for identifying gene regulatory elements (e.g., elements within the regulatory, non-coding sequences of the CARK gene) that modulate cardiac gene transcription during hypertrophic growth. EXAMPLE 3: Expression of Recombinant CARK Protein in Bacterial Cells In this example. CARK is expressed as a recombinant glutathione-S-transferase (GST) fusion polypeptide in E. coli and the fusion polypeptide is isolated and characterized. Specifically, CARK is fused to GST and this fusion polypeptide is expressed in E. coli, e.g., strain PΕB199. Expression ofthe GST-CARK fusion protein in PEB 199 is induced with IPTG. The recombinant fusion polypeptide is purified from crude bacterial lysates ofthe induced PEB 199 strain by affinity chromatography on glutathione beads. Using polyacrylamide gel electrophoretic analysis ofthe polypeptide purified from the bacterial lysates, the molecular weight of the resultant fusion polypeptide is determined. EXAMPLE 4: Expression of Recombinant CARK Protein in COS Cells To express the CARK gene in COS cells, the pcDNA/Amp vector by Invitrogen Coφoration (San Diego, CA) is used. This vector contains an SV40 origin of replication, an ampicillin resistance gene, an E. coli replication origin, a CMV promoter followed by a polylinker region, and an SV40 intron and polyadenylation site. A DNA fragment encoding the entire CARK protein and an HA tag (Wilson et al. (1984) Cell 37:767) or a FLAG tag fused in-frame to its 3' end ofthe fragment is cloned into the polylinker region ofthe vector, thereby placing the expression ofthe recombinant protein under the control ofthe CMV promoter. To construct the plasmid, the CARK DNA sequence is amplified by PCR using two primers. The 5' primer contains the restriction site of interest followed by approximately twenty nucleotides ofthe CARK coding sequence starting from the initiation codon; the 3' end sequence contains complementary sequences to the other restriction site of interest, a translation stop codon, the HA tag or FLAG tag and the last 20 nucleotides of the CARK coding sequence. The PCR amplified fragment and the pCDNA/Amp vector are digested with the appropriate restriction enzymes and the vector is dephosphorylated using the CIAP enzyme (New England Biolabs, Beverly. MA). Preferably the two restriction sites chosen are different so that the CARK gene is inserted in the correct orientation. The ligation mixture is transformed into E. coli cells (strains HB101. DH5a, SURE, available from Stratagene Cloning Systems, La Jolla. CA, can be used), the transformed culture is plated on ampicillin media plates, and resistant colonies are selected. Plasmid DNA is isolated from transformants and examined by restriction analysis for the presence of the correct fragment. COS cells are subsequently transfected with the CARK-pcDNA/Amp plasmid DNA using the calcium phosphate or calcium chloride co-precipitation methods, DEAE- dextran-mediated transfection, lipofection, or electroporation. Other suitable methods for transfecting host cells can be found in Sambrook, J., Fritsh, E. F., and Maniatis, T. Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989. The expression ofthe CARK polypeptide is detected by radiolabelling ( 35 S-methionine or 35 S-cysteine available from NEN, Boston, MA, can be used) and immunoprecipitation (Harlow, E. and Lane, D. Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1988) using an HA specific monoclonal antibody. Briefly, the cells are labelled for 8 hours with 35 S-methionine (or 35 S-cysteine). The culture media are then collected and the cells are lysed using detergents (RIPA buffer, 150 mM NaCl, 1% NP-40, 0.1% SDS, 0.5% DOC, 50 mM Tris, pH 7.5). Both the cell lysate and the culture media are precipitated with an HA specific monoclonal antibody. Precipitated polypeptides are then analyzed by SDS-PAGE. Alternatively, DNA containing the CARK coding sequence is cloned directly into the polylinker ofthe pCDN A/Amp vector using the appropriate restriction sites. The resulting plasmid is transfected into COS cells in the manner described above, and the expression of the CARK polypeptide is detected by radiolabelling and immunoprecipitation using a CARK specific monoclonal antibody. Equivalents Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

Claims: What is claimed: 1. An isolated nucleic acid molecule selected from the group consisting of: (a) a nucleic acid molecule comprising the nucleotide sequence set forth in SEQ ID NOJ or 7; and (b) a nucleic acid molecule comprising the nucleotide sequence set forth in SEQ ID NOJ or 9. 2. An isolated nucleic acid molecule which encodes a polypeptide comprising the amino acid sequence set forth in SEQ ID NO: 2 or 8. 3. An isolated nucleic acid molecule comprising the nucleotide sequence contained in the plasmid deposited with ATCC® as Accession Number . 4. An isolated nucleic acid molecule which encodes a naturally occurring allelic variant of a polypeptide comprising the amino acid sequence set forth in SEQ ID NO: 2 or 8. 5. An isolated nucleic acid molecule selected from the group consisting of: a) a nucleic acid molecule comprising a nucleotide sequence which is at least 60%o homologous to the nucleotide sequence of SEQ ID NOJ, 3, 7, or 9, or a complement thereof; b) a nucleic acid molecule comprising a fragment of at least 467 nucleotides of a nucleic acid comprising the nucleotide sequence of SEQ ID NO: 1, 3, 7, or 9, or a complement thereof; c) a nucleic acid molecule which encodes a polypeptide comprising an amino acid sequence at least about 60%> homologous to the amino acid sequence of SEQ ID NO:2 or 8: and d) a nucleic acid molecule which encodes a fragment of a polypeptide comprising the amino acid sequence of SEQ ID NO:2 or 8, wherein the fragment comprises at least 15 contiguous amino acid residues ofthe amino acid sequence of SEQ ID NO:2 or 8. 6. An isolated nucleic acid molecule which hybridizes to the nucleic acid molecule of any one of claims 1, 2, 3, 4, or 5 under stringent conditions. 7. An isolated nucleic acid molecule comprising a nucleotide sequence which is complementary to the nucleotide sequence ofthe nucleic acid molecule of any one of claims 1. 2. 3. 4, or 5. 8. An isolated nucleic acid molecule comprising the nucleic acid molecule of any one of claims 1. 2, 3, 4, or 5, and a nucleotide sequence encoding a heterologous polypeptide. 9. A vector comprising the nucleic acid molecule of any one of claims 1 , 2. 3, 4, or 5. 10. The vector of claim 9, which is an expression vector. 1 1. A host cell transfected with the expression vector of claim 10. 12. A method of producing a polypeptide comprising culturing the host cell of claim 1 1 in an appropriate culture medium to, thereby, produce the polypeptide. 13. An isolated polypeptide selected from the group consisting of: a) a fragment of a polypeptide comprising the amino acid sequence of SEQ ID NO:2 or 8, wherein the fragment comprises at least 15 contiguous amino acids of SEQ ID NO:2 or 8; b) a naturally occurring allelic variant of a polypeptide comprising the amino acid sequence of SEQ ID NO:2 or 8, wherein the polypeptide is encoded by a nucleic acid molecule which hybridizes to a nucleic acid molecule consisting of SEQ ID NOJ, 3. 7, or 9 under stringent conditions; c) a polypeptide which is encoded by a nucleic acid molecule comprising a nucleotide sequence which is at least 60 % homologous to a nucleic acid comprising the nucleotide sequence of SEQ ID NOJ, 3, 7, or 9; d) a polypeptide comprising an amino acid sequence which is at least 60%) homologous to the amino acid sequence of SEQ ID NO:2 or 8. 14. The isolated polypeptide of claim 13 comprising the amino acid sequence of SEQ ID NO:2 or 8. 15. The polypeptide of claim 13, further comprising heterologous amino acid sequences. 16. An antibody which selectively binds to a polypeptide of claim 13. 17. A method for detecting the presence of a polypeptide of claim 13 in a sample comprising: a) contacting the sample with a compound which selectively binds to the polypeptide; and b) determining whether the compound binds to the polypeptide in the sample to thereby detect the presence of a polypeptide of claim 13 in the sample. 18. The method of claim 17, wherein the compound which binds to the polypeptide is an antibody. 19. A kit comprising a compound which selectively binds to a polypeptide of claim 13 and instructions for use. 20. A method for detecting the presence of a nucleic acid molecule of any one of claims 1, 2, 3, 4, or 5 in a sample comprising: a) contacting the sample with a nucleic acid probe or primer which selectively hybridizes to the nucleic acid molecule; and b) determining whether the nucleic acid probe or primer binds to a nucleic acid molecule in the sample to thereby detect the presence of a nucleic acid molecule of any one of claims 1, 2, 3, 4, or 5 in the sample. 21. The method of claim 20, wherein the sample comprises mRNA molecules and is contacted with a nucleic acid probe. 22. A kit comprising a compound which selectively hybridizes to a nucleic acid molecule of any one of claims 1, 2, 3, 4, or 5 and instructions for use. 23. A method for identifying a compound which binds to a polypeptide of claim 13 comprising: a) contacting the polypeptide, or a cell expressing the polypeptide with a test compound; and b) determining whether the polypeptide binds to the test compound. 24. The method of claim 23, wherein the binding ofthe test compound to the polypeptide is detected by a method selected from the group consisting of: a) detection of binding by direct detection of test compound/polypeptide binding; b) detection of binding using a competition binding assay; and c) detection of binding using an assay for CARK activity. 25. A method for modulating the activity of a polypeptide of claim 13 comprising contacting the polypeptide or a cell expressing the polypeptide with a compound which binds to the polypeptide in a sufficient concentration to modulate the activity ofthe polypeptide. 26. A method for identifying a compound which modulates the activity of a polypeptide of claim 13 comprising: a) contacting a polypeptide of claim 13 with a test compound; and b) determining the effect ofthe test compound on the activity of the polypeptide to thereby identify a compound which modulates the activity ofthe polypeptide.

Inventors: RAJU JEYASEELAN, RAJU, JEYASEELAN
Applicants: MILLENNIUM PHARM INC, MILLENNIUM PHARMACEUTICALS, INC.
Application year: 1999
Main classification: C07K14
IPC codes: A61K38, A61K39, A61K45, A61P9, A61P35, A61P43, C07K16, C12N1, C12N5, C12N9, C12N15, C12Q1, G01N33