Association of a tyrosine kinase activity with GAP complexes in v-src transformed fibroblasts

Abstract

p21ras GAP is phosphorylated on tyrosine residues and associates with 62 kDa and 190 kDa tyrosine phosphorylated proteins in v-src-transformed fibroblasts. We were interested in identifying the tyrosine kinase responsible for phosphorylation of GAP and the two associated proteins. Here, we report that GAP-immunoprecipitates from v-src transformed cells contain a tyrosine kinase activity that phosphorylates GAP, p62 and p190. Tryptic peptide analysis indicated that the sites phosphorylated in vitro and in vivo are indistinguishable, suggesting that the precipitated kinase could be responsible for tyrosine phosphorylation of GAP in vivo. The GAP-associated kinase activity might be due to v-src itself, because pp60v-src is able to associate with GAP in vitro and GAP can be phosphorylated by pp60v-src immunecomplexes.