Phosphorylation of JAK2 in Dami/HEL and Mo7e cells. (A) Cellular proteins (500 μg/mL) from untreated Dami/HEL or Mo7e cells (CTL), or from cells treated with 400 ng/mL TPO or 40 ng/mL IL-3, were precipitated with antiphosphotyrosine agarose. The immunoprecipitates were subjected to SDS-PAGE, transferred to PVDF membrane, and probed with antihuman JAK2 antibody to detect tyrosine-phosphorylated JAK2. (B) Cellular proteins (20 μg) from untreated Dami/HEL or Mo7e cells (CTL), or cells treated with 400 ng/mL TPO or 40 ng/mL IL-3, were subjected directly to 7.5% SDS-PAGE and the blotted PVDF membrane was probed with antihuman JAK2 antiserum to detect total JAK2 protein as a control. Molecular mass markers are indicated in kilodaltons.