Whole-cell extracts containing overexpressed PR from baculovirus-infected insect cells were incubated with the −273, −230, −197, or −139 probes and tested for complex formation in EMSA. Antibodies (Ab) are indicated with the left lane containing no antibody (−), the middle lane containing PR antibody (PR), and the right lane containing a nonspecific IgG control antibody (IgG). The antibody supershift is marked with an arrowhead.