Fig. 5.
Syk and ZAP-70 are phosphorylated with similar kinetics in T-cell lines, whereas only Syk is phosphorylated in transduced U937/ZAP-70 cells. The Jurkat 77-6.8 T-cell line, an HTLV-I–transformed T-cell line MB, U937 cells, and two pools of ZAP-70–transduced cells (U937/ZAP-70a and U937-ZAP-70b ) were stimulated with a CD3 (for T cells) or FcγRI MoAb (for U937 cells) for the indicated times. Lysates were immunoprecipitated with either an anti-Syk (upper panel) or an anti–ZAP-70 antibody (lower panel), fractionated on a polyacrylamide gel, and immunoblotted with an antiphosphotyrosine antibody. Blots were then reprobed with either an anti-Syk (upper panel) or anti–ZAP-70 antibody (lower panel). The positions of Syk and ZAP-70 are indicated with arrows and the positions of molecular weight markers are noted. These data are representative of results obtained in six independent experiments.