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 [γ- 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°C but not at 39°C. Anti-p30 immune complexes from 6m2 cells maintained at 39°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°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°C but not at 39°C. Since 6m2 cells at 39°C contain P58 gag , this is also consistent with the kinase activity being associated with P85 gag-mos . gag-mos phosphoprotein phosphotransferase retrovirus transforming protein