Demonstration of a DNA-protein complex in the MS7 region of β₃. (A) Location of the MS6 and MS7 probes and the putative binding site for the Sp1 transcriptional factor. (B) EMSA using ³²P-labeled MS7 DNA probe and the indicated nuclear extracts. Cold specific or irrelevant oligonucleotide competitors (Table 1) were used at a 50-fold molar excess. Irr., irrelevant DNA competitor; c, unlabeled oligonucleotide.