Detection of an additional CDP-binding site in the proximal gp91^phox promoter. EMSA was performed as described in Materials and Methods, with the MIN binding site as a probe, nuclear extract derived from HeLa cells, and 10 ng of the homologous competitor oligonucleotide and equimolar amounts of the other competitor oligonucleotides derived from the gp91^phox promoter. The Spi-B oligonucleotide is included as a heterologous competitor. EMSA was performed by using the −39 to −1 bp region of the gp91^phox promoter as probe. CDP-ɛ is used as a probe in the first lane to provide a size standard for the CDP complex. Reactions contained nuclear extract derived from either PLB-985 cells induced to terminally differentiate into granulocytes (lane 9) or HeLa cells as indicated. Reactions also contain 100 ng of homologous oligonucleotide (or equimolar amounts of other competitor oligonucleotides) (lanes 6-8), antiserum directed against CDP (lane 3), or normal guinea pig serum (lane 4) where indicated. Lanes from a single gel were rearranged during figure preparation for clarity of presentation.