GM-CSF induction of GAS-binding complexes in BM-derived macrophages from STAT5A null, HZ, and WT mice. BM-derived macrophages from null (−/−; lanes 1 and 4), HZ (+/−; lanes 2 and 5), and WT (+/+; lanes 3 and 6) mice were incubated with either medium (lanes 1-3) or 10 ng/mL of GM-CSF (lanes 4-6) for 15 minutes at 37°C, and whole cell extracts (5 μg of protein per lane) were analyzed by EMSA using the ³²P-labeled β-casein probe as described in Materials and Methods. Arrows labeled a, b, and c indicate the uppermost, middle, and lowermost bands containing GAS-binding complexes, respectively.