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A chromatin fraction, which can reproducibly be extracted from rat liver nuclei at moderate salt concentration (0.1 M (NH)SO, 0.1 M Tris-HCl, 2 mM MnCl, pH 7.9), was analyzed with regard to changes of its molecular weight in the range of (NH)SO concentrations between 0.1 M and 0.4 M. With the transition from 0.1 M to 0.2 M (NH)SO histone H1 is released and the molecular weight obtained from both sedimentation-viscosity and light scattering is reduced by approximately one-half. A spatial expansion of the resulting half-molecules is observed with further increasing salt concentration. On the basis of these results a double-fibrillar structure of this chromatin fraction is proposed. [ABSTRACT FROM AUTHOR]

The mass per unit length of $$7X10^3 \frac{9}{{Mol \cdot \mathop A\limits^ \circ }}$$ and the corresponding DNA packing ratio of about 14 for the chromatin soluble at moderate ionic strengths has been determined by light scattering. With the increase in ionic strength and corresponding release of histone H1 the DNA packing ratio has been found to decrease down to 4.4. The data obtained are consistent with the idea suggested previously that the salt-soluble chromatin is organized in double nucleosome chains arranged side-by-side and stabilized by H1. With salt-induced H1 release the double chain dissociates and the nucleosomal DNA partially unravels. [ABSTRACT FROM AUTHOR]

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)SO 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)SO. 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)SO. [ABSTRACT FROM AUTHOR]