DNA-binding proteins that interact with the −68 to −30 bp gp91^phox promoter. EMSA was performed as described in Materials and Methods using the −68 to −30 bp region of the gp91^phox promoter as a probe. Probe was incubated with 3 μg of nuclear extract isolated from PLB985, U937, and Jurkat cells after preincubation with a 100-fold molar excess of unlabeled double-stranded competitor oligonucleotide where indicated. The left-hand autoradiogram is overexposed to visualize the faint faster-migrating complex. A shorter exposure is presented below to resolve the HAF-1/CP1 doublet. None, no competitor added; Homo, competitor oligonucleotide homologous to probe; −55 CGD, same as Homo, except containing a T to C mutation at position −55 bp; −57 CGD, same as Homo, except containing an A to C mutation at −57 bp; PU.1, competitor oligonucleotide containing a binding site for PU.127; Elf-1, competitor oligonucleotide containing a binding site for Elf-126; Heter, heterologous oligonucleotide corresponding to E36, a high-affinity binding site for CDP.28 The positions of the HAF-1 and PU.1 complexes are indicated by arrows.