Use of site-specific antipeptide antibodies to perturb the serine kinase catalytic activity of p37mos.

The mos oncogene of Moloney murine sarcoma virus encodes a protein of approximately 37,000 daltons (designated p37mos). We have detected a serine protein kinase activity which is closely associated with p37mos in immune complexes obtained with antibodies [anti-mos(37-55) serum] that were generated with a peptide containing amino acids 37 through 55 of the v-mos protein (S. A. Maxwell and R. B. Arlinghaus, Virology 143:321-333, 1985). Immune complexes that were derived with antibodies generated against peptides representing the C-terminal 8 or 12 amino acids of v-mos (anti-C2 and anti-C3 serum, respectively) exhibited very little kinase activity capable of phosphorylating p37mos. Treatment of anti-mos(37-55) complexes containing active v-mos kinase with anti-C3 or anti-C2 serum resulted in a dramatic reduction of the in vitro phosphorylation of p37mos. Antiserum blocked with the appropriate C-terminal peptide had no inhibitory effect on the phosphorylation of p37mos in anti-mos(37-55) complexes which indicated that the inhibition of v-mos kinase activity was a specific effect of these antibodies. The specific inhibition of the in vitro phosphorylation of p37mos by antibodies directed against the C terminus of the v-mos protein provides strong evidence that the v-mos gene encodes a serine protein kinase. In addition, the extreme C terminus of p37mos may be critical for an active v-mos kinase.