Fig. 1. STAT1 DNA binding is activated by IFN- in both MCF-7 and MDA-MB-231 cells. A, MCF-7 and MDA-MB-231 whole cell lysates were treated with and without 10 ng/ml IFN- and incubated with the labeled probe representing a STAT1 consensus binding site from the c-fos promoter. A431 cells treated with 30 ng/ml EGF were included as a positive control for STAT1 and STAT3 binding. Complexes were resolved by PAGE and autoradiography. B, MCF-7 and MDA-MB-231 whole cell lysates were incubated with labeled probe, and antibodies to STAT1 or STAT2 were added. Complexes were resolved by PAGE and visualized by autoradiography. Only STAT1 antibodies resulted in a supershift of the complex.