Phosphorylation of the ras GTPase-activating protein (GAP) by the p93c-fes protein-tyrosine kinase in vitro and formation of GAP-fes complexes via an SH2 domain-dependent mechanism

The protein-tyrosine kinase encoded by the human c- fes protooncogene (p93 c-fes ) plays a direct role in myeloid differentiation, but downstream substrates for this kinase have not been identified. Here we report that the human ras GTPase-activating protein (GAP) is a substrate for p93 c-fes in vitro. Purified, recombiriant GAP was readily phosphorylated on tyrosine residues by bacterially-expressed p93 c-fes . Two-dimerisional tryptic mapping revealed a single GAP phosphopeptide, consistent with specific phosphorylation of GAP by p93 c-fes on one or several closely-spaced tyrosine residues. Autophosphorylated p93 c-fes also formed a stable complex with GAP