Solubilization of nuclear structures by the polyanion heparin.

Rat liver nuclei were treated with different concentrations of the polyanion heparin, at low ionic strength and in the absence of divalent cations. Heparin at the optimal concentration (Heparin:DNA greater than or equal to 1) completely solubilized the intranuclear structures, allowing the preparation of pure nuclear membranes. The majority of the nuclear proteins, including all of H1 and 70% of the core histone oligomers, were solubilized. By contrast, suboptimal concentrations of heparin (heparin:DNA less than 0.3) resulted in the selective solubilization of non-histone proteins and the partial solubilization of chromatin without dissociation of histones from DNA. Among the RNA- and DNA-associated non-histone proteins revealed by the heparin fractionation procedure, some are noteworthy. A DNA-associated protein of 40,000 daltons was found to be associated with core histone oligomer. Three proteins of Mr = 62,000, 70,000, and 74,000, identical with that of the lamina proteins, were distinguished by their presence in all the fractions obtained, their predominance in the less soluble fractions, and their tight association with DNA and RNA. More than the solubilization of the histones, their extraction seems to be a prerequisite for chromatin solubilization by heparin.