Presence of complexes binding onto the −455 flanking region. To detect complexes that may potentially bind onto the −455 nucleotide and its proximal 5′ and 3′ flanking regions, two 34-bp oligonucleotide probes were used in EMSA analysis having the sequence of the Bβ chain from −468 to −439. The probes contained either a guanine (G-455) or an adenine (A-455) in the −455 position. EMSA results resolved on 7% nondenaturing gels show three complexes binding onto the radiolabeled probes when either an adenine (A-455), representing the A allele (A, lanes 1 through 5), or a guanine (G-455), representing the G allele (B, lanes 6 through 10), is present. To assess the specificity of the bound complexes, both probes were competed with increasing concentrations of unlabeled probe: 0-fold, 10-fold (4 ng), 100-fold (40 ng), 250-fold (100 ng), and 500-fold (200 ng) excess the radiolabeled probe concentration. Both competition assays, radiolabeled A-455 versus unlabeled A-455 (lanes 1 through 5) and radiolabeled G-455 versus unlabeled G-455 (lanes 6 through 10), show that all three complexes are binding onto both probes specifically; however, complexes II and III appear to bind more specifically.