SKBr3 cells were transfected with the Spi 2.1 promoter luciferase construct and either wtSTAT5b, Y740/743F, S731A, or S731A/Y740/743F. Luciferase activity from unstimulated cells was measured as described in “Experimental Procedures.” The graph represents three independent experiments with each group in each experiment done in triplicate. Values are reported as fold induction over wtSTAT5b (con) ± S. E. They are: wtSTAT5b (1.00 ± 0.00); Y740/743F (2.36 ± 0.79); S731A (1.36 ± 0.12); S731A/Y740/743F (0.38 ± 0.02). Student’s t test was utilized to determine statistical significance between Y740/743F and S731A/Y740/743F in addition to wtSTAT5b and S731A/Y740/743F. *, p< 0.001 ●, p<0.001.