Complex III preferentially binds to the G allele. (A) In the cross-competition assays, performed to detect preferential allelic binding of the complexes, when radiolabeled A-455 probe is competed against increasing concentrations of unlabeled G-455 probe (lanes 1 through 5), the three complexes are able to be competed away from the radiolabeled A-455 probe, with competition patterns similar to the results in Fig 2. Complex III is not competed away from radiolabed G-455 by increasing concentrations of A-455 unlabeled competitor (lanes 6 through 10), even at 1,000-fold cold competitor (data not shown), as seen in the three previous competition assays, implying that complex III preferentially binds to the G allele or a guanine in the −455 position. (B) Decrease in band intensity of complex III at increasing concentrations of cold competitor was analyzed by scanning densitometer analysis to observe the strength with which the unlabeled competitiors competed against the radiolabeled probes. Results for all of the competition assays were comparable with the exception of the labeled G-455 probe versus unlabled A-455 probe competition assay. The unlabeled A-455 competitor was unable to competitively bind with complex III in the presence of labeled G-455 at the same rate as the other competition assays, also showing that complex III preferentally binds to the G allele, rather than to the A allele. The assays were resolved on 7% nondenaturing gels. (○), Labeled A-455 probe versus unlabeled A-455 probe; (•), labeled A-455 probe versus unlabeled G-455 probe; (□), labeled G-455 probe versus unlabeled G-455 probe; (▪), labeled G-455 probe versus unlabeled A-455 probe.