The Partial Dissociation of Nucleohistone by Salts. Hydrodynamic and Denaturation Studies

Calf thymus deoxyribonucleohistone was partially depleted of histone in salt solutions and the viscosity, sedimentation and thermal denaturation properties of the depleted samples were measured. The histones removed were characterised by polyacrylamide gel electrophoresis. Both the viscosity and sedimentation studies show DNA to be considerably more asymmetric than nucleohistone. This increase in asymmetry has been shown to be associated with the removal of the f2b, f2a2 and f3 fractions from the nucleohistone. It is concluded that at least one of these fractions maintains the DNA in a supercoil in the native nucleohistone. All the histone fraction stabilised the DNA to thermal denaturation. A biphasic melting profile was observed for native deoxyribonucleohistone, which became monophasic on the removal of the same histone fractions as those implicated in supercoiling.