(A) Flow cytometric analysis of sorted NBM cells. CD71⁻ and GPA⁻ cells (rectangle 1), CD71⁺ and GPA⁻ cells (rectangle 2), CD71⁺ and GPA⁺ cells (rectangle 3), CD71⁻ and GPA⁺ cells (rectangle 4). (B) STAT5 activation in NBM cells sorted for CD71 and GPA expression. Cells sorted according to the windows in (A) (0, unsorted cells [lanes 1 through 3]; 1, CD71⁻ and GPA⁻ cells [lanes 4 through 6]; 2, CD71⁺ and GPA⁻ cells [lanes 7 through 9]; 3, CD71⁺ and GPA⁺ cells [lanes 10 through 12]; and 4, CD71⁻ and GPA⁺ cells [lanes 13 through 15]) were obtained and extracted after 15 minutes of incubation without factor (lanes 1, 4, 7, 10, 13), with IL-3 (lanes 2, 5, 8, 11, 14), or with Epo (lanes 3, 6, 9, 12, 15). Nuclear extracts were incubated with the β-casein probe and analyzed for activation of STAT5 on a nondenaturing polyacrylamide gel. Arrow indicates position of STAT5 complex.