Site-Specific Increased Phosphorylation of pp60 v- src After Treatment of RSV-Transformed Cells with a Tumor Promoter

When vole cells that had been transformed by Rous sarcoma virus were treated with the tumor-promoting phorbol ester 12- O -tetradecanoyl-13-acetate (TPA), specific phosphorylation of pp60 v- src was increased. Partial V8 protease mapping indicated that the increased phosphorylation occurred exclusively on serine residues located in the amino terminus of the molecule. Treatment of cells with dimethyl sulfoxide or 4α-phorbol-12,13-didecanoate did not elicit this response. Two-dimensional tryptic phosphopeptide mapping of pp60 v- src immunoprecipitated from untreated and TPA-treated cells indicated that a specific tryptic amino-terminal peptide was hyperphosphorylated.