Involvement of histone H1 in the organization of the chromosome fiber.

At high ionic strength (e.g., physiological salt concentrations) chromosome fibers are 200 A in diameter and composed of discrete globular structures that are held together by histone H1. At low ionic strength the fibers unfold and appear as the familiar chains of nucleosomes (80 A in diameter). The unfolding of chromosome fibers occurs within a narrow salt range. It results from a change in the mode of the interaction between histone H1 and the chromosome fiber and is very likely the consequence of a change from cooperative binding between histone H1 and DNA to a noncooperative binding. In the noncooperative binding state histone H1 molecules are randomly redistributed along the chromosome fiber.