The v-mos protein, termed p37v-ms, has a closely associated serine/threonine protein kinase activity. To provide further information about its protein kinase activity, we tested the activity of p37V-"s produced in a cell-free translation system from transcripts generated from a cloned v-mos gene. Anti-mos(37-55) immunoprecipitates of in vitro-produced p37V-?Os were found to possess serine/threonine protein kinase activity, whereas those obtained with anti-mos(260-271), known to block v-mos

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... hosphorylation, lacked kinase activity. The phosphorylated products were identical in size to p37vrn0s and p43v-mos produced in protein kinase assays from Moloney murine sarcoma virus-infected cells expressing authentic p37v.°s. These results provide further proof that the protein kinase activity associated with p37v.mos is an intrinsic property of the v-mos gene product. This translation system also provides a useful experimental model to study the activation of the mos protein kinase. Thus, protein kinase assays performed on [35S]methionine-labeled p37v-ms produced p43v'm-s at the expense of p37v-ms. Phosphatase treatment removed the p43V-mos species, resulting in an increase of the p37VrMos-sized protein, confirming our previous interpretation that p43Vm0s is a hyperphosphorylated form of p37v-mos The transforming protein encoded by the viral mos (vmos) gene of Moloney murine sarcoma virus (Mo-MuSV)-124 is an env-mos fusion protein (termed p37v-rns) with a on May 8, 2020 by guest