P34(CD2) PROTEIN IS COMPLEXED WITH THE C-MOS PROTEIN IN RAT SKELETAL-MUSCLE

We have used fractionation of subcellular components of the skeletal m uscle followed by Western blot analyses to study the localization of t he c-mos protein in adult rat muscle. We find that p43c-mos is predomi nantly located in the KCl supernatant fraction. We show that immunopre cipitates of p43c-mos phosphorylate in vitro two polypeptides of about 34 kDa and 80 kDa respectively. Muscle fractionation and immunodetect ion studies showed that the p34 protein associated with p43c-mos is th e cdc2 protein. p43c-mos is coprecipitated with p34cdc2 when using eit her anti PSTAIR antibody, antibody directed against the conserved COOH terminal region of the p34cdc2 and by binding to beads that contain c rosslinked p13suc1, a protein known to bind p34cdc2. Likewise p34cdc2 coprecipitated with p43c-mos when using anti mos antibody. However p43 c-mos is not present in histone H1 kinase active p34cdc2 complex preci pitated with anti p34cdc2 COOH-terminal peptide antibody. In adult mus cle tissue tubulin is not complexed with p34cdc2 and p43c-mos as previ ously observed in c-mos and v-mos transformed cells. Gel filtration an d crosslinking experiments show that a 170 kDa complex contains c-mos and p34cdc2 proteins. In addition during postnatal development of skel etal muscle we observe modifications in the migration pattern of p34cd c2 correlated with the accumulation of p43c-mos. Our findings raise th e possibility of a p43c-mos-p34cdc2 complex could play a role in the d ifferentiation process and maintenance of myotubes in Go.