The Lnk SH2 domain is required to inhibit Epo-induced JAK2 and EpoR phosphorylation. Primary erythroblasts transduced with either vector alone, or wild-type Lnk or the SH2 mutant (R364E) were immunoprecipitated with anti-EpoR (A), or anti-JAK2 (B) or anti-Lnk (C) antibodies, and probed with antiphosphotyrosine (4G10) antibodies. Total protein levels are shown in the bottom panels.