Physicochemical properties of salt-soluble, unsheared chromatin. Salt-dependent structural changes.

Salt-dependent structural changes of rat liver chromatin isolated by an extraction procedure not involving shear and exogenous nucleases were investigated by sedimentation and light scattering methods. The effects observed are complex involving changes in the molecular weight and expansion. Between 0.1 M and 0.2 M (NH4)2SO4 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 (NH4)2SO2. 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 (NH4)2SO4.