Quasielastic light-scattering studies on dinucleosomal-sized DNA: ionic-strength dependence.

Abstract

AbstractQuasielastic light‐scattering (QELS) studies were performed on a monodisperse preparation of dinucleosomal‐sized DNA having an average of 375 base pairs. The QELS data were obtained at several time intervals at each angle examined over the range 30° < θ < 60° for the ionic strength solvents 500, 50, 10, and 1 mM in KCl. What results from this study is that two relaxation domains persist over the entire ionic strength range where the “splitting” between these two domains increases as the ionic strength is lowered. The ordinate intercept of Dapp vs Cp/2Cs, where Cp is the polyion concentration and Cs is the added salt concentration, is shown to give the “true” hydrodynamic value for the diffusion coefficient. The “splitting phenomenon” is interpreted in terms of two models currently in vogue: small ion–polyion coupled modes and translational–rotational coupled modes for rigid rods in congested solutions. Although neither model is in perfect agreement with the experimental results, the small ion–polyion coupled mode theory appears to provide a better quantitative description of the observations.