Erythropoietin activates STAT5 in erythroid cells. Growth factor-deprived day-8 cells were stimulated with 10 U/mL erythropoietin and nuclear extracts were prepared. Nuclear extracts were subject to EMSA by using a β-casein probe. Lane 1, nuclear extracts from unstimulated cells; lane 2, nuclear extracts from erythropoietin-stimulated cells; lane 3, the same as in lane 2, except the nuclear extracts were incubated with STAT5 antisera before EMSA. Shift indicates probe complex in the absence of the antibodies. Super Shift indicates the supershifted band in the presence of STAT5 antisera.