Charge transport through DNA four-way junctions

Long range oxidative damage as a result of charge transport is shown to occ ur through single cross-over junctions assembled from four semi-complementa ry strands of DNA. When a rhodium complex is tethered to one of the arms of the four-way junction assembly, thereby restricting its intercalation into the pi -stack, photo-induced oxidative damage occurs to varying degrees at all guanine doublets in the assembly, though direct strand scission only o ccurs at the predicted site of intercalation. In studies where the Mg2+ con centration was varied, so as to perturb base stacking at the junction, char ge transport was found to be enhanced but not to be strongly localized to t he arms that preferentially stack on each other. These data suggest that th e conformations of four-way junctions can be relatively mobile. Certainly, in four-way junctions charge transport is less discriminate than in the mor e rigidly stacked DNA double crossover assemblies.