Study of DNA conformation in native, partial and reconstituted nucleohistones, using hydrodynamic methods and optical rotatory dispersion.

Abstract

Abstract 1. 1. The course of the intrinsic viscosity of DNA in native, partial and reconstituted nucleohistones and the correlation of the hydrodynamic parameters s° and [η] support the conclusions reached concerning the compact character of nucleohistone particles, in agreement with the assumed superstructure of DNA. No significant differences in the character of particles of partial and reconstituted nucleohistones were found. The degree of compactness of the particles appears to be determined by the ratio histone DNA rather than by the nature of the histone in the complex. 2. 2. The optical rotatory dispersion (ORD) spectra of native, partial and reconstituted nucleohistones were compared in 0.01 M Tris buffer, where the complex is intact, and in 2 M NaCl where the complex is largely dissociated. An examination of the ORD spectra of DNA in nucleohistones indicated that these spectra were different from the spectrum of free DNA. The difference was the same for DNA in partial and reconstituted nucleohistones and depended only on the ratio of protein to DNA. The deviations of the ORD spectra of DNA can best be explained by a slight change in the parameters of the DNA double helix accompanying supercoil formation.