The avian sarcoma virus transforming gene product has been identified and partially purified from extracts of transformed cells. It is a phosphoprotein with a relative molecular mass of 60 000 (pp60
src
) with two major sites of phosphorylation. pp60
src
appears to be a cyclic-AMP-independent protein kinase as judged by protein phosphorylation with partly purified fractions. The specificity of the phosphorylation observed was judged by inhibition with anti-pp60
src
IgG but not by normal IgG and by the fact that the protein kinase activity isolated from
ts
transformation-mutant infected cells was more thermolabile than that from wild-type transformed cells, thus showing more directly the origin of the enzymic activity. A cellular protein substrate of pp60
src
has been identified as a 34000 molecular mass protein. These data together suggest that protein phosphorylation by pp60
src
may be a function of the molecule that plays a major role in transformation.
Biochemical characterization of pp60src-associated protein kinase from avian sarcoma virus Schmidt-Ruppin strain.
