Conformational changes in supercoiled DNA: 111In-histone as a label for perturbed γ–γ angular correlation studies

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Abstract
Conformational changes induced in superhelical PM2 DNA by addition of the intercalating dye ethidium bromide have been observed by the technique of perturbed γ–γ angular correlations. Using 111In‐histone as a probe, rotational correlation times were determined for dye to DNA nucleotide ratios of zero (τc = 8.2±0.6 ns), 5:1 (τc = 2.2±0.2 ns), and 25:1 (τc = 4.9±0.4 ns). These features are related to the superhelical turn density of the molecule. The theoretical fits also indicate the presence of components with shorter time fluctuations (≲1 ns).