Ectopic ZAP-70 and Syk expression are associated with distinct TCR-ζ phosphorylation profiles in p116 Jurkat cells. p116 Jurkat cells (ZAP^–/Syk^–) expressing equivalent levels of ectopic ZAP-70 (ZAP^E/Syk^–) or Syk (ZAP^–/Syk^E) (Figure 2) were stimulated via CD3 cross-linking (3′) or pervanadate (VO₄)(5′). Immunoprecipitations were performed with an αTCR-ζ Ab, and the levels of the p21 and p23 phosphorylated TCR-ζ isoforms as well as the nonphosphorylated p16 isoform following stimulation are shown. The presence of ζ-associated ZAP-70 and Syk molecules as well as their relative phosphorylation status were determined by immunoblotting the ζ immunoprecipitates with αZAP-70, αSyk, and αPY Abs, respectively.