Deletion of the SH2 domains abrogates the FcεRI-mediated tyrosine phosphorylation of plasma membrane–associated Syk.

Cell lines expressing different forms of Syk were stimulated with antigen (Ag), and cell lysates were then immunoprecipitated with anti-Syk antibody. Immunoprecipitates were analyzed by immunoblotting with antiphosphotyrosine (pTyr) (top) and anti-Syk antibodies (bottom). Similar results were obtained when the other cloned lines were tested in 5 independent experiments.