Src homology 2 (PFAM:PF00017) , SH2 domain, was initially found as a conserved sequence area shared by Src and Fps oncoproteins. The SH2 domain is the regulatory module of the intracellular signal cascade. It is sequence-specific and interacts with the target peptide containing phosphotyrosine to recognize the 3-6 residues at the C-terminal phosphorylated tyrosine. The SH2 domain is distinct from the others in that it is phosphorylation-dependent. Tyrosine kinases are associated with the catalytic domain of phospholipase Cy (PLCy) and non-receptor proteins. They often bind monophosphorylated and diphosphorylated substrates in structural proteins such as fibrin and tensin. Phorbol ester (PE) is a DAG analog that acts as a potent tumor promoter, causing a variety of physiological alterations in cells and tissues when injected.