ZAP70 is a 70-kD tyrosine phosphoprotein that associates with the zeta chain and undergoes tyrosine phosphorylation following TCR stimulation. The ZAP70 gene is expressed in T- and natural KILLER cells. Protein-Tyrosine Kinases (PTKs) play an integral role in T-cell activation. Stimulation of the T-cell antigen receptor results in tyrosine phosphorylation of a number of cellular substrates. One of these is the TCR-zeta chain, which can mediate the transduction of extracellular stimuli into cellular effector functions
