Lck-mediated phosphorylation of CD33.

(A) 293T cells were transfected with Lck, kinase dead Lck (Lck^K273R), Syk, kinase dead Syk (Syk^K395R), Zap70 or kinase dead Zap70 (Zap70^K369R), and wild-type CD33 cDNA. After 24 hours, cells were lysed, immunoprecipitated with anti-CD33, and immunoblotted with anti-phosphotyrosine antibody (upper panel). (B) 293T cells were transfected with the indicated CD33 cDNA and Lck kinase then analyzed as in A. In both cases, expression of CD33 was verified using flow cytometry (data not shown) and immunoblotting of parallel samples with anti-CD33 (lower panels).