A 50 KILODALTON PROTEIN ASSOCIATED WITH RAF AND PP(60V-SRC) PROTEIN-KINASES IS A MAMMALIAN HOMOLOG OF THE CELL-CYCLE CONTROL PROTEIN CDC37

Several oncogenic protein kinases including c-raf-1 and pp60(v-src) ar e known to directly interact with the 90 kDa heat shock protein (hsp90 )/p50 complexes. Using a monoclonal antibody to detect p50 during a pu rification scheme, p50 was purified to homogeneity. Internal amino aci d sequence information was obtained and used to clone a partial cDNA., Comparison of the p50 sequence to other cloned proteins revealed 89% homology with a glycosaminoglycan-binding protein and 54% homology wit h Drosophila cell cycle control protein (cdc) 37., Monoclonal and poly clonal antibodies were produced against a cleaved fusion protein that recognizes p50 with a high level of specificity, These antibodies reco gnize the 50 kDa protein present in c-raf-l and pp60(v-src) complexes, No other proteins were recognized with these antibodies suggesting th at p50 is a unique protein. Immunocytochemical visualization of p50 in NIH 3T3 cells indicates a primarily cytoplasmic localization around t he nuclear membrane, A survey of p50 expression in murine tissue on a protein blot revealed thp following relative levels of expression; thy mus > spleen > brain > heart > kidney > liver > lung > skeletal muscle . These results link studies demonstrating complexation of certain kin ases with hsp90/p50 in mammalian cells and a number of reports in yeas t and Drosophila, demonstrating the importance of cdc37 in cell cycle and kinase function.