Epo induces the tyrosine phosphorylation of GAB1 in normal erythroid progenitors isolated from human cord blood. A purified population of human erythroid progenitor cells was prepared as described in Materials and Methods. The cells were serum- and growth factor-deprived by overnight incubation in Iscove’s DMEM containing 0.4% deionized BSA and 25 μg/mL iron-saturated human transferrin. The cells were then stimulated (+) or not (−) for 10 minutes with 10 U/mL Epo. Lysates from 20 × 10⁶ cells were immunoprecipitated with anti-GAB1 antibodies and analyzed by Western blot using antiphosphotyrosine (anti-PY) and anti-GAB1 antibodies, successively.