Fractionation of two protein kinases from avian myeloblastosis virus and characterization of the protein kinase activity preferring basic phosphoacceptor proteins

Abstract

Two protein kinase activities were fractionated from purified virions of avian myeloblastosis virus. Distinguishing characteristics of these two protein kinases included: (i) their binding properties during purification by ion-exchange chromatography; (ii) their estimated molecular weights; and (iii) their phosphoacceptor protein specificities. The protein kinase that bound to the anion exchanger DEAE-cellulose (pH 7.2) had an estimated molecular weight of 60,000 to 64,000 and preferred basic phosphoacceptor proteins. The protein kinase that bound to the cation exchanger phosphocellulose (pH 7.2) had an estimated molecular weight of 42,000 to 46,000 and preferred acidic phosphoacceptor proteins. The protein kinase preferring basic phosphoacceptor proteins was further purified and characterized. Optimal transfer of phosphate catalyzed by this enzyme required a divalent metal ion, a sulfhydryl-reducing agent, and ATP as phosphate donor. GTP was not an effective phosphate donor at concentrations comparable to ATP; and the cyclic nucleotides cyclic AMP and cyclic GMP neither stimulated nor inhibited protein phosphorylation by the protein kinase. The specificity of the protein kinase for basic phosphoacceptor proteins extended to proteins from avian myeloblastosis virus, in that the neutral to basic virion proteins p12, p19, and p27 served as phosphate acceptors. In addition, the protein kinase also appeared to phosphorylate itself. The role(s) of this virion-associated protein kinase is discussed.