MAPPING OF SITES ON THE SRC FAMILY PROTEIN-TYROSINE KINASES P55BLK, P59FYN, AND P56LYN WHICH INTERACT WITH THE EFFECTOR MOLECULES PHOSPHOLIPASE C-GAMMA-2, MICROTUBULE-ASSOCIATED PROTEIN-KINASE, GTPASE-ACTIVATING PROTEIN, AND PHOSPHATIDYLINOSITOL 3-KINASE

Engagement of the B-cell antigen receptor complex induces immediate ac tivation of receptor-associated Src family tyrosine kinases including p55blk, p59fyn., p53/56lyn, and perhaps p56lck, and this response is a ccompanied by tyrosine phosphorylation of distinct cellular substrates . These kinases act directly or indirectly to phosphorylate and/or act ivate effector proteins including p42 (microtubule-associated protein kinase) (MAPK), phospholipases C-gamma1 (PLCgamma1) and C-gamma2 (PLC- gamma2), phosphatidylinositol 3-kinase (PI 3-K), and p21ras-GTPase-act ivating protein (GAP). Although coimmunoprecipitation results indicate that the Src family protein tyrosine kinases interact physically with some of these effector molecules, the molecular basis of this interac tion has not been established. Here, we show that three distinct sites mediate the interaction of these kinases with effectors. The amino-te rminal 27 residues of the unique domain of p56lyn mediate association with PLC-gamma2, MAPK, and GAP. Binding to PI 3-K is mediated through the Src homology 3 (SH3) domains of the Src family kinases. Relatively small proportions of cellular PI 3-K, PLC-gamma2, MAPK, and GAP, pres umably those which are tyrosine phosphorylated, bind to the SH2 domain s of these kinases. Comparative analysis of binding activities of Blk, Lyn, and Fyn shows that these kinases differ in their abilities to as sociate with MAPK and PI 3-K, suggesting that they may prererentially bind and subsequently phosphorylate distinct sets of downstream effect or molecules in vivo. Fast protein liquid chromatography Mono Q column -fractionated MAPK maintains the ability to bind bacterially expressed Lyn, suggesting that the two kinases may interact directly.