Mutually enhanced binding affinities of Sp1 and Wt1(–KTS) to the human EPO promoter. EMSA demonstrating that Wt1 and Sp1 enhance the binding of each protein to the identified EPO promoter element (oligonucelotide –66/–37). Lane 1, oligonucelotide alone. In lane 2, 1 μg recombinant Wt1(–KTS) isoform was added to the reaction. Note that increasing concentrations of recombinant Sp1 protein (100 ng, 200 ng, 300 ng, 400 ng, 500 ng, 1 μg; lanes 3-8, respectively) enhanced Wt1(–KTS) binding to the DNA. Conversely, Sp1/DNA complex formation was improved with increasing concentrations of Wt1(–KTS) protein (100 ng, 200 ng, 300 ng, 400 ng, 500 ng, 1 μg; lanes 10-15, respectively). Protein complexes were resolved on a 5% polyacrylamide gel, and complex formation was visualized after 48 hours by autoradiography.