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We have used gel electrophoresis to measure the progress of local denaturation in closed circular pBR322 DNA as a function of temperature and linking deficiency, delta Lk. Local denaturation is closely coupled to supercoiling in closed DNA, requiring statistical mechanical methods for analysis. We have applied these methods to the experimental data to(More)
The twist is a fundamental geometric property of nucleic acids. Calculation of the twist in the most general case requires detailed specification of the three-dimensional path of each strand, but many important cases may be analyzed by considering only the twist difference. If C1, C2, and C3 are three distinct space curves, the twist difference about C1 is(More)
The interaction of platinum and palladium complexes with closed and nicked circular and linear DNAs was investigated by a variety of methods. Cationic metal complexes containing flat, aromatic ligands, such as 2,2',2''-terpyridine, o-phenanthroline, and 2,2'-bipyridine, interfere with the usual fluorescence enhancement of ethidium bromide by competing for(More)
We have measured the helical repeat of acetylated nucleosomes reconstituted with HeLa cell histone octamers and the 5 S RNA gene positioning sequence from Xenopus borealis. The hydroxyl radical footprinting experiments show that the helical repeat of nucleosome-bound DNA is unchanged upon acetylation, and that the extent of DNA-protein contacts remains(More)
Vaccinia virus cores contain an activity which is able to relax both left-and right-handed superhelical DNA. This virus-specific nicking closing enzyme has been highly purified and differs from the corresponding host enzyme in salt optimum, in sedimentation coefficient, and in polypeptide composition as determined on sodium dodecyl sulfate/polyacrylamide(More)
Time-correlated single-photon counting of intercalated ethidium bromide was used to measure the torsion constants of positively supercoiled, relaxed, and negatively supercoiled pBR322 DNA, which range in superhelix density from +0.042 to -0.123. DNA behaves as coupled, nonlinear torsional pendulums under superhelical stress, and the anharmonic term in the(More)