Time course of STAT5 binding in Ba/F3-EpoR and Ba/F3 -IL-5α/β_IL3 cells. (A) Ba/F3-EpoR cells were maintained in Epo (0.5 U/mL) washed 3× in PBS and starved for 6 hours in RPMI medium containing 10% FCS. Cells were then stimulated with either IL-3 (0.5 ng/mL) or Epo (0.5 U/mL) for the indicated period of time (1 × 10⁷ cells per time point). Nuclear extracts were obtained and used for an EMSA with a β-casein probe as described in Materials and Methods. (B) Ba/F3-IL-5α/β_IL3 were maintained in IL-5 (1 ng/mL) and treated as above. Stimulation was performed with either IL-3 (0.5 ng/mL) or IL-5 (1 ng/mL).