p140 is a new phosphotyrosyl protein. (A) Cell lysates from unstimulated (lanes 1 and 3) or hGM-CSF–stimulated (lanes 2 and 4) TF-1 cells were immunoprecipitated with anti-Jak2 (lane 1 and 2) or anti-Shc (lanes 3 and 4) antibodies and analyzed by antiphosphotyrosine immunoblotting (lanes 1 through 4). The positions of Jak2, Shc, p140, and Ig heavy chain (Ig) are indicated. (B) Cell lysates from unstimulated (lanes 1 and 3) or hGM-CSF–stimulated (lane 2 and 4) TF-1 cells were immunoprecipitated with antibodies directed against Shc (lanes 1 and 2) or the β subunit of the human GM-CSF receptor (β-GMR; lanes 3 and 4) and analyzed by antiphosphotyrosine immunoblotting (lanes 1 through 4).