p34cdc2 protein is complexed with the c-mos protein in rat skeletal muscle

We have used fractionation of subcellular components of the skeletal muscle followed by Western blot analyses to study the localization of the c-mos protein in adult rat muscle. We find that p43c-mos is predominantly located in the KCl supernatant fraction. We show that immunoprecipitates of p43c-mos phosphorylate in vitro two polypeptides of about 34 kDa and 80 kDa respectively. Muscle fractionation and immunodetection studies showed that the p34 protein associated with p43c-mos is the cdc2 protein. p43c-mos is coprecipitated with p34cdc2 when using either anti PSTAIR antibody, antibody directed against the conserved COOH terminal region of the p34cdc2 and by binding to beads that contain cross-linked p13suc1, a protein known to bind p34cdc2. Likewise p34cdc2 coprecipitated with p43c-mos when using anti mos antibody. However p43c-mos is not present in histone H1 kinase active p34cdc2 complex precipitated with anti p34cdc2 COOH-terminal peptide antibody. In adult muscle tissue tubulin is not complexed with p34cdc2 and p43c-mos as previously observed in c-mos and v-mos transformed cells. Gel filtration and crosslinking experiments show that a 170 kDa complex contains c-mos and p34cdc2 proteins. In addition during postnatal development of skeletal muscle we observe modifications in the migration pattern of p34cdc2 correlated with the accumulation of p43c-mos. Our findings raise the possibility of a p43c-mos-p34cdc2 complex could play a role in the differentiation process and maintenance of myotubes in Go.