Tyr527 is phosphorylated in pp60c-src: implications for regulation.

The Rous sarcoma virus oncogene product, pp60v-src, transforms cultured fibroblasts but its corresponding proto-oncogene product, pp60c-src, does not. Both proteins are known to be protein-tyrosine kinases. Published results suggest that the kinase activity of pp60c-src is inhibited relative to that of pp60v-src, due perhaps to phosphorylation of a tyrosine in pp60c-src that is not phosphorylated in pp60v-src. In this study, it was observed that the tyrosine phosphorylated in pp60c-src is Tyr527, six residues from the COOH-terminus of the protein. The region of pp60c-src from residue 515 to the COOH-terminus, including Tyr527, has been replaced with a different sequence in pp60v-src. Thus, the increase in transforming ability and kinase activity that occurred in the genesis of pp60v-src may have resulted from the loss of a tyrosine involved in negative regulation.