FIG. 3.

LAT tyrosine phosphorylation is lost in Syk- but not in SLP-76-deficient mouse platelets and Btk-deficient (XLA) human platelets. Platelets were stimulated with CRP (3 μg/ml) for 2 min and then lysed by addition of an equal volume of ice-cold NP-40 buffer. After preclearing, samples were immunoprecipitated for LAT as described in Materials and Methods. Membranes were probed for tyrosine phosphorylation (top panel) and reprobed for LAT (bottom panel). The arrows indicate the migration of the immunoprecipitated protein. LAT was immunoprecipitated from Syk-deficient mouse platelets (a), SLP-76-deficient mouse platelets (b), and Btk-deficient human platelets (c). Results are from one experiment representative of three. p-Tyr, phosphotyrosine.