Anti-pp60src antibodies are substrates for EGF-stimulated protein kinase

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Abstract
Epidermal growth factor (EGF) stimulates phosphorylation of its own receptor at a tyrosine residue. Similarly, the viral gene product pp60src, which is responsible for cellular transformation by avian sarcoma virus (ASV), phosphorylates itself and Ig directed against pp60src at tyrosine residues. This unusual site of phosphorylation catalyzed by 2 membrane-associated protein kinases involved in growth control prompted a study of the immunological relatedness of the EGF-stimulated protein kinase and the pp60src. Using anti-pp60src antisera, an attempt was made to immunoprecipitate the EGF-stimulated protein kinase solubilized from plasma membranes (of human carcinoma A431 cells). Neither the EGF-stimulated kinase nor the EGF receptor were immunoprecipitable by anti-pp60src sera. Anti-pp60src IgG served as a specific substrate for the EGF-stimulated kinase, suggesting a close similarity between the EGF-stimulated kinase and pp60src.