P85gag-mos encoded by ts110 Moloney murine sarcoma virus has an associated protein kinase activity.

A protein identified as P85(gag-mos) was shown to be phosphorylated when immunoprecipitates from ts110 Moloney murine sarcoma virus transformed nonproducer cells (clone 6m2) were incubated with [gamma-(32)P]ATP. The in vitro-labeled 85,000-dalton phosphoprotein comigrated on NaDodSO(4)/polyacrylamide gels with authentic phosphorylated P85(gag-mos). Immunoprecipitates obtained with antisera prepared against Rauscher murine leukemia virus core protein p30 were active in the immune complex kinase assay but anti-murine leukemia virus p10 precipitates were not. Previous studies have shown that anti-p30 but not anti-p10 antisera recognize P85(gag-mos). The 6m2 clone has been shown to express P85(gag-mos) at 33 degrees C but not at 39 degrees C. Anti-p30 immune complexes from 6m2 cells maintained at 39 degrees C failed to phosphorylate the 85,000-dalton protein. Furthermore, the in vitro phosphorylated 85,000-dalton protein gave the same pattern of V8 protease-generated cleavage products as in vivo(32)P-labeled P85(gag-mos). We conclude from these results that P85(gag-mos) is phosphorylated in anti-p30 immune complex kinase reactions. Phosphoamino acid analyses indicated that the in vitro phosphorylated P85(gag-mos) contained phosphoserine and phosphothreonine. Our findings indicate that incubation of anti-p30 immunoprecipitates at 39 degrees C drastically reduced, in a specific way, the kinase activity associated with P85(gag-mos). This result and other data suggest that the kinase is virus-encoded. Because P85(gag-mos), but not Pr65(gag) is phosphorylated in anti-p30 immunoprecipitates from MuLV-MuSV ts110 producer cells, the kinase enzyme is associated with P85(gag-mos) and not gag gene products. A second major polypeptide of the size of P58(gag) was also phosphorylated in anti-p30 immunoprecipitates from cells maintained at 33 degrees C but not at 39 degrees C. Since 6m2 cells at 39 degrees C contain P58(gag), this is also consistent with the kinase activity being associated with P85(gag-mos).