Physicochemical Properties of Salt-Soluble, Unsheared Chromatin

Salt-dependent structural changes of rat liver chromatin isolated by an extraction procedure not involving shear and exogeneous nucleases were investigated by sedimentation and light scattering methods. The effects observed are complex involving changes of the molecular weight and expansion. Between 0.1 M and 0.2 M (NH sub(4)) sub(2)SO sub(4) where histone H1 is released, a fragmentation into molecules of half molecular weight is found which is accompanied by an expansion into a more extended conformation gradually increasing to 0.4 M (NH sub(4)) sub(2)SO sub(4). The H1-free chromatin does not exhibit the reduction in molecular weight but undergoes this expansion. The original conformation is not reversible on re-decreasing the salt concentration to 0.1 M (NH sub(4)) sub(2)SO sub(4).