Evidence that a phosphotyrosine-containing 120,000 Da protein from Rous sarcoma virus-infected cells is...

Phosphorylation of a phosphotyrosine-containing 120,000 Da protein (pp120) in Rous sarcoma virus (RSV)-infected mammalian cells and in in vitro protein kinase reactions was examined. Phosphorylated pp120 was co-immunoprecipitated with anti-pp60v-src antibodies only from RSV-transformed or revertant vole fibroblasts which contained active pp60v-src tyrosine kinase activity or from temperature-sensitive RSV-infected vole cells grown at the permissive temperature. Pp120 was phosphorylated on tyrosine in in vitro immune complex kinase reactions containing both pp120 and enzymatically active pp60v-src. Inhibition of pp60v-src's kinase activity blocked phosphorylation of pp120 in vitro. These results support the proposal that pp120 tyrosine phosphorylation is pp60v-src-dependent and that pp120 may thus serve as a substrate of pp60v-src in RSV-transformed mammalian cells.