Themes in Signaling   Binding of the SH2 domains of PLC to tyrosine autophosphorylation sites in activated receptors facilitates tyrosine phosphorylation of PLC as well as membrane translocation; a process medi ated in part by binding of the PH domain to products of PI-3 kinase. Tyrosine phosphorylation is essential for PLC activation leading to hydrolysis of PtdIns(4,5)P2 and the generation of the two second messengers Ins(1,4,5)P3 and diacylglycosol.