TANDEM SH2 DOMAINS OF ZAP-70 BIND TO T-CELL ANTIGEN RECEPTOR-ZETA ANDCD3-EPSILON FROM ACTIVATED JURKAT T-CELLS

A proximal and critical biochemical event upon T cell antigen receptor (TCR) stimulation is the activation of a protein tyrosine kinase (PTK ) pathway. ZAP-70, a PTK of the p72syk family, associates with phospho rylated TCR subunits upon TCR stimulation. Here we report that the tan dem SH2 domains of ZAP-70, expressed as a fusion protein, bind to tyro sine-phosphorylated CD3epsilon and TCRzeta from activated Jurkat T cel l lysates. The single N- and C-terminal SH2 domains of ZAP-70, express ed separately, do not bind these TCR subunits. In comparison to fusion proteins containing SH2 domains from other proteins, the tandem SH2 d omains of ZAP-70 demonstrate a remarkably restricted repertoire of pro tein binding, binding only TCRzeta and CD3epsilon. ZAP-70 is also reco vered in the binding assay, but this is likely to be a consequence of its interaction with multiple SH2 binding sites on the zeta-zeta and C D3epsilon-containing dimers.