The compatibility of netropsin and actinomycin binding to natural deoxyribonucleic acid

The simultaneous binding of netropsin and actinomycin to four natural DNAs was studied to determine the influence of one ligand on the binding of the other. Actinomycin binds specifically to GC sites, whereas netropsin binds specifically to AT sites. Spectral titrations, thermal denaturation, and analytical buoyant density centrifugation were employed to measure the binding interference of these drugs. The binding of actinomycin to DNA was decreased by the presence of netropsin. Increasing the GC content of the DNA resulted in a decreased effect of netropsin on actinomycin binding. Quantitative analysis of the binding parameters indicated that netropsin and actinomycin can bind in close proximity along the DNA chain. Supercoiled DNA gave the same result as linear DNA. These results imply that DNA can absorb alterations in conformation within a short distance.