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Virus particles of the Schmidt-Ruppin strain, subgroup D (SR-D), contain the sarcoma virus-coded transformation-specific protein pp60"'" and its associated protein kinase.Using purified virus particles as source of pp60"'", it was purified about thousandfold by ion exchange column chromatography, gel filtration on Sephadex G-150, and glycerol density gradient centrifugation.The protein kinase activity was assayed for by in vitro phosphorylation of the immunoglobin (IgG) of tumor-bearing rabbit (TBR) serum, a-casein, actin, and by endogenous phosphorylation with subsequent immunoprecipitation with TBR serum.The pp60"'" associated protein kinase was one of four virion-associated kinase activities.It specifically phosphorylated the amino acid tyrosine of substrate proteins.The IgGphosphorylating activity co-purified predominantly with a molecule of 45,000 molecular weight, which was shown to be related to pp60"'" by partial proteolytic cleavage.During endogenous phosphorylation reactions, pp60" or the 45,000 fragment were phosphorylated in tyrosine.In the absence of nonionic detergents, pp60"'" tended t o form aggregates of up to 2 X lo6 molecular weight depending on purity, detergent, and protein concentration.The aggregate phosphorylated pp60"" during endogenous phosphorylation but not IgG.Only after mild proteolytic treatment they recovered the ability of phosphorylating IgG of TBR serum.An ATPase activity assayed for by ATP hydrolysis was co-purified with the sarcoma-specific protein kinase through two ion exchange chromatographies but was separated off by size fractionation.A single step partial purification of pp60"'" protein kinase activity was achieved by using viral membranes as starting material.In vitro phosphorylation in tyrosine was observed with substrates such as actin, histones H5, H4, and the cytoskeleton protein vinculin.The transforming gene product of avian sarcoma viruses was detected in transformed fibroblasts by precipitation with sera from tumor-bearing rabbits.It was shown to be a phosphoprotein of 60,000 molecular weight, designated pp60"", which is associated with a protein kinase.The enzyme phosphorylates the heavy chain of the immunoglobulin of TBR' serum, to which it is bound (1-4).We have recently shown that pp60"" and its associated
Donner et al. (Sat,) studied this question.