The protein in the −93/−84 complex has the binding specificity and mobility of Sp1. (A) A 2-bp mutation (GGGGCGTGGC > GGTTCGTGGC) was introduced into the −93/−84 Sp1 site of the XN2 oligonucleotide (XN2mt), and binding ability was compared with the wild-type XN2 oligonucleotide. The −/+ indicates whether cellular extract was added to the gel shift mixture. Ten thousand cpm of the XN2 and XN2mt oligonucleotides were incubated with 10 μg of H526 extract. (B) Mobility shift of XN2 oligonucleotide with rhSp1. Mobility shift analysis using the XN2 oligonucleotide incubated with H526 extract (10 μg ) or with recombinant human Sp1 (rhSp1, 1 fpu) and Drosophila nuclear extract (1 μg). Incubation of the XN2 oligonucleotide with H526 extract (lane 2) yielded a band with a similar mobility pattern as that obtained by incubating XN2 oligonucleotide with rhSp1 andDrosophila extract (lane 3). Incubation of XN2 oligonucleotide with Drosophila extract alone was used as a negative control (lane 4).