Synthetic peptide fragment of src gene product inhibits the src protein kinase and crossreacts immunologically with avian onc kinases and cellular phosphoproteins.

All the known avian sarcoma viruses have associated protein kinase activities that phosphorylate tyrosine residues of their target proteins. A decapeptide fragment of pp60src of Rous sarcoma virus (RSV), residues 415-424, and an analog of that sequence have been chemically synthesized by solid-phase methods. The two decapeptides were not phosphorylated by pp60src of RSV, P90 of Y73 avian sarcoma virus, or P140 of Fujinami sarcoma virus. However, both peptides were able to inhibit competitively the kinase activities associated with the transforming proteins. Antiserum was raised against one of the peptides and IgG was purified from the serum by affinity chromatography. The antibody was able to precipitate pp60src of RSV as well as P90 of Y73 virus from cells infected with these viruses. The antibody also precipitated a number of high molecular weight phosphoproteins from normal chicken and rat fibroblasts and from several lines of virus-transformed cells.