| To define further the molecular mechanism by which CD 22 mediates its co receptor function , phosphopeptide mapping experiments were conducted to determine which of the six tyrosine residues in the cytoplasmic domain are involved in recruitment of the stimulatory effector proteins phospholipase Cgamma ( PLCgamma ) , phosphoinositide 3 kinase ( PI3K ) , Grb 2 , and Syk . ^^^ Although both PLCgamma and PI3K were observed to bind to multiple phosphopeptides in precipitation experiments , subsequent studies using reverse Far Western blot analysis demonstrated that only the carboxyl terminal phosphopeptide of CD 22 ( Y863VTL ) binds directly to either one . ^^^ This finding suggests that PLCgamma and PI3K may be recruited to CD 22 either through a direct interaction with Tyr 863 or indirectly through an association with one or more intermediate proteins . . ^^^ |