FIG. 6.

Phosphorylation of 21- and 90-kDa substrates but not of Syk in TCR-induced MT-2 cells. Jcl20 or MT-2 cells were stimulated for the indicated periods of time with anti-TCR MAb Vit-3 and subsequently lysed in Nonidet P-40 containing buffer. (A) Proteins (50 μg) from whole-cell lysates were separated on 8% (top panel) or 12% (bottom panel) SDS-PAGE gels and probed with antiphosphotyrosine antibody. The 90- and 21-kDa tyrosine phosphorylated proteins are indicated by arrowheads. The positions of prestained molecular-mass markers are shown on the right. (B) With the same extracts, anti-Syk immunoprecipitation was followed by antiphosphotyrosine immunoblotting (top panel) or anti-Syk immunoblotting (bottom panel). The positions of Syk and the heavy chain of IgG (Ig) are indicated on the left, while the molecular-mass markers are shown on the right.