Evidence for interaction between v-Mos and a p34^cdc2 isoform, p35^cdk

The c-mos gene product (c-Mos) encodes a serine/ threonine kinase required for activation of pre-MPF (maturation-promoting factor) to MPF in oocytes undergoing meiosis and also for stabilization of MPF leading to metaphase arrest in unfertilized eggs. In order to determine whether the v-mos gene product (v-Mos) causes neoplastic transformation via interaction with cell cycle control elements, we have searched for proteins that interact with v-Mos. Extracts of NIH3T3 cells transformed by v-Mos encoded by Moloney murine sarcoma virus (Mo-MuSV) were examined by gel filtration, by immunoprecipitation with antibodies to a conserved region of p34^cdc2 and by binding to beads that contain cross-linked p13^suc1 a protein known to bind p34^cdc2. Gel filtration detected a 500-kDa complex that contained v-Mos and a p34^cdc2 isoform, termed p35^cdk. The 500-kDa macromolecular complex also exhibited histone H1 phosphorylation activity, consistent with the presence of a cdc2 isoform. The identity of p35^cdk is based on its recognition by anti-cdc2 PSTAIR but not by anti-cdc2 C-terminal antibodies, which detect authentic p34^cdc2. Structures containing v-Mos and p35^cdk were also detected by experiments involving co-immunoprecipitation of v-Mos with anti-cdc2 PSTAIR antibodies. Furthermore, both v-Mos and the p35^cdk co-precipitated with p13^suc1-Sepharose beads. Our findings raise the possibility of a v-Mos-p35^cdk regulatory interaction in cells transformed by Mo-MuSV.