TEL-Jak2 expression does not activate tyrosine phosphorylation of Jak1, Jak2, or Jak3. (A) Ba/F3 (lanes 1 through 6) or Ba/F3 HA-TEL-Jak2 JH1 subclone 36 (lanes 7 through 12) cells were depleted of cytokine and stimulated in the presence or absence of IL-3. Immunoprecipitations were performed with a pan-specific Jak antibody, a Jak1 antibody, or a Jak2 antibody. Tyrosine-phosphorylated proteins were detected by immunoblotting with a monoclonal antiphosphotyrosine antibody. The migration of endogenous Jak proteins and TEL-Jak2 JH1 and molecular weight standards are indicated. (B) Ba/F3 (lanes 1 and 2) or Ba/F3 HA-TEL-Jak2 JH1 subclone 36 (lanes 3 and 4) or CTLL (lanes 5 and 6) cells were depleted of cytokine and stimulated in the presence or absence of IL-3 (lanes 1 through 4) or IL-2 (lanes 5 and 6). Immunoprecipitations were performed with a Jak3 antibody. Tyrosine-phosphorylated proteins were detected as described above.