The global tyrosine phosphorylation pattern after FcγRI clustering is not affected by ZAP-70 expression. Uninfected U937 cells or U937 cells expressing Neo (LN) or ZAP-70 were either unstimulated (−) or cross-linked with an FcγRI MoAb (+). Lysates were fractionated by gel electrophoresis and immunoblotted with antiphosphotyrosine antibodies. These data are representative of results obtained in six independent experiments.