Swelling of nuclei and decondensation of chromatin in a multinuclear model.

Rat liver nuclei were isolated in the presence of a nonionic detergent, and the soluble proteins were extracted from them using low-salt solution. The isolated nuclei were then embedded in a fibrin clot which was cut into 4 to 5 mm3 pieces and placed into an AMICON pressure cell in the presence and absence of the soluble nuclear proteins. When the soluble nuclear proteins were present and when their concentrations reached 40 mg/ml, the nuclei were significantly larger and their chromatin more decondensed than in the absence of added proteins. Our findings suggest that the soluble nuclear proteins play a role in the regulation of nuclear volume and the hydration of chromatin.