Competition between oligonucleotides −52C or −52T and a consensus Sp1 oligonucleotide (Sp1*).

The positions of complexes I, II, and III are indicated to the left of the gel. Nuclear extracts were prepared from Dami cells and incubated with radiolabeled oligonucleotides (Table 2) either in the absence of inhibitor (lane 1) or following preincubation with a 20-fold molar excess (lanes 2, 3) or 200-fold molar excess (lanes 4, 5) of Sp1* (Promega). Radiolabeled Sp1* forms a complex with Sp1 derived from Dami cell nuclear protein extracts (lane 6) that has a mobility identical to that of complex II formed with probes −52C (“C”) or −52T (“T”); the complex formed with labeled Sp1* is also inhibited by addition of a 200-fold molar excess of unlabeled Sp1* (lane 7).