CONFORMATION OF LIDNA IN SOLUTIONS OF LICL

Radii of gyration, Rg, were derived from the absolute intensity of the scattered light of monodisperse linear Col E1 LiDNA in solution at various LiCl concentrations up to 5 M. The 2nd virial coefficients, A2, decrease strongly with increasing LiCl concentration, and vanish between 3 and 5 M LiCl. It was thus possible to calculate a limiting value at a high salt concentration of 28.5 nm for the persistence length, .alpha.0, of LiDNA, without the necessity of applying excluded-volume corrections. The value obtained is in good agreement with the value previously obtained for NaDNA at high NaCl concentrations, and can be identified with the high salt limit of DNA flexibility, with long-range electrostatic interactions effectively screened. Sedimentation coefficients in the ultracentrifuge and apparent and translational diffusion coefficients (at finite and vanishing scattering vectors, respectively) from dynamic laser-light scattering were also obtained up to 5 M LiCl. From the sedimentation and apparent diffusion, D(90) (at 90.degree. scattering angle only) above 5 M, and up to 9 M LiCl, it could be shown that the solutions are stable for reasonable periods of time, and the molecular parameters vary smoothly and moderately at high salt. Conformational transitions were not observed and precipitation occurs between 9 and 10 M LiCl.