Protein kinase activity associated with immunoprecipitates of the vesicular stomatitis virus phosphoprotein NS

Monospecific antisera prepared to denatured N and NS proteins of the Indiana serotype of VSV were used to investigate the protein associations in extracts of virus-infected cells. Complexes precipitated from the cytoplasm of infected cells with either anti-N or anti-NS serum both contained N and NS proteins but could be differentiated by the absence of any trace of M protein in the complexes precipitated with anti-NS serum. Immunoprecipitation with anti-NS serum of NS protein from the soluble cytoplasmic protein pool always resulted in coprecipitation of N protein suggesting a possible functional association of these proteins in the soluble fraction. The association of protein kinase activity with complexes containing NS protein was demonstrated by the phosphorylation of NS serine residues when immunoprecipitates containing NS protein were incubated with [32P]ATP in vitro. In protein aggregates precipitated with antibody after high salt dissociation of viral proteins it was also possible to demonstrate the presence of a c-src-like protein kinase activity as previously shown by G.M. Clinton, N.G. Guerina, H. Guo, and H.S. Huang (J. Biol. Chem. 257, 3313-3319 (1982) ).