Structurally and functionally modified forms of pp60v-src in Rous sarcoma virus-transformed cell lysates.
When analyzed from transformed cell lysates, pp60v-src, the product of the Rous sarcoma virus src gene, typically appears as a single polypeptide of 60,000 molecular weight, phosphorylated at two major sites, an amino-terminal region serine residue and carboxy-terminal region tyrosine residue. We describe here the identification of variant forms of pp60v-src present in transformed cell lysates that exhibited an altered electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gels. This change in migration appeared to be the result of some alteration in the amino-terminal portion of the molecule and paralleled the appearance of extensive amino-terminal region tyrosine phosphorylation on the pp60v-src molecule. These structural modifications were further correlated with a dramatic increase in the protein kinase-specific activity of pp60v-src. The detection of these variant forms of pp60v-src depended on the prior treatment of the transformed cell cultures with vanadium ions or the inclusion in the cell disruption buffer of Mg2+ or ATP-Mg2+. The implications is that modified, highly active forms of the pp60v-src protein exist in transformed cells, but are transient and rapidly converted to stable forms, possibly by specific dephosphorylation. We suggest that amino-terminal region tyrosine phosphorylation of pp60v-src, presumably the result of autophosphorylation, serves to greatly enhance src protein enzymatic activity, but that much of the regulation of this transforming protein's function may involve a phosphotyrosyl protein phosphatase.
D000818:Animals; D003411:Arvicolinae; D001358:Avian Sarcoma Viruses / Q000235:genetics*; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D005814:Genes, Viral; D015688:Oncogene Protein pp60(v-src); D010446:Peptide Fragments / Q000032:analysis; D010748:Phosphopeptides / Q000032:analysis; D011494:Protein Kinases / Q000235:genetics*; D014764:Viral Proteins / Q000235:genetics* / Q000302:isolation & purification
D010446:Peptide Fragments; D010748:Phosphopeptides; D014764:Viral Proteins; D011494:Protein Kinases; D015688:Oncogene Protein pp60(v-src)