Time course of the induction of β-globin mRNAs by SB and Epo. Parental Ba/F3 cells were treated with 1 mmol/L SB. E-7, a clone of Ba/F3 cells transfected with the EpoR and selected with G418, responds to both the mitogenic and differentiation-inducing effects of Epo.2 E-7 cells in IL-3–containing medium were washed three times with RPMI 1640 medium containing 10% FBS and exposed to 0.5 U/mL of Epo. RNA was subjected to northern hybridization with β^major-globin, ɛ-globin, and actin probes.