FIG. 9.

The cellular transcription factor Sp1 binds to the IR1 element. U373-IE86 nuclear extracts were incubated with a radiolabeled IR1 oligonucleotide and a 50-fold excess of unlabeled IR1, CREB, or Sp1 competitor oligonucleotides (panel A, lanes 2 to 4, respectively) or 1 μg of polyclonal antibodies specific for ATF, CREB, or Sp1 (panel B, lanes 2 to 4, respectively). U373-IE86 nuclear extract alone was used as a control (lanes 1). The unlabeled arrows indicate specific complexes. SS, supershifted complex.