Transforming gene product of avian sarcoma viruses and its homolog in uninfected cells.

The product of the avian sarcoma virus (ASV) transforming gene is a 60,000-dalton phosphoprotein, pp60src. Sera from mice and from an occasional rabbit bearing ASV-induced tumors are capable of immunoprecipitating a phosphoprotein of similar, but not identical, structure from normal avian and mammalian cells. This protein is presumed to be the product of the cellular sarc gene, and has been tentatively designated pp60sarc. Analysis of the tryptic phosphopeptides reveals that the viral and avian proteins have an apparently identical phosphoserine-containing peptide. They evidently also both have an analogous phosphothreonine residue surrounded by a different amino acid sequence. Immunoprecipitates containing either the viral or normal cellular pp60 protein catalyze the transfer of radiolabeled phosphate from [gamma-32P]-ATP to the heavy chain of immune rabbit IgG, therefore suggesting that both viral and cellular phosphoproteins may be protein kinases.