Figure 5.

Effects of site-directed mutations on SYK kinase activity. A, the basal kinase activity of each unphosphorylated mutant SYK was evaluated relative to the WT protein using the Omnia kinase assay. Enzyme (4 nm), ATP (35 μm), and peptide (10 μm) concentrations were kept constant in all reactions. B, the basal kinase activity of each phosphorylated mutant SYK was evaluated relative to the WT protein. Reaction conditions are identical to those of A. C, Western blots (region migrating at 65–80 kDa) examining site-specific SYK tyrosine phosphorylation of unphosphorylated and prephosphorylated WT and mutant SYK proteins. Conditions are described under “Experimental procedures.”