Effect of polyanions on the structure of rat liver nuclear chromatinстатья
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Дата последнего поиска статьи во внешних источниках: 28 мая 2015 г.
Местоположение издательства:Road Town, United Kingdom
Первая страница:677
Последняя страница:685
Аннотация:Stepwise effects of polyanions (heparin and dextran sulfate) on interphase rat liver chromatin were studied. Polyanions (PA) first induce chromatin condensation at PA/DNA ratio 0.125, then decondensation into 10 nm fibrils at PA/DNA = 0.2, and finally recondensation into 30-50 nm fibrils and compact globular particles (GP) 40-70 nm in diameter at PA/DNA > 0.3. Subsequent addition of ammonium acetate to 0.15-0.5 M converts the whole material of the nucleus into a regular network of GP linked by DNA-containing fibrils. The diameter of the GP (40-70 nm) does not change in the PA/DNA interval from 0.4 to 1.5. The nuclei with GP retain 85-90% of the DNA and 50-70% of the protein. Treatment of the GP-containing nuclei with staphylococcal nuclease revealed the absence of nucleosomal periodicity in DNA organization. Nuclei treated with PA and salt in the presence of EDTA retain the core histones of the nucleosomes and those treated with Mg2+ also retain histone H1. The most compact GP are obtained at pH 6.0-6.5. At pH 5.0 and 8.5 the GP partially unfold into tangles of granules 10 nm in diameter linked by thin fibrils. Dialysis against low ionic strength solutions in the presence of EDTA reversibly unfold the nuclear GP into a fibrillar-granular network. Increasing PA/DNA above 1.5 or treatment of the GP-containing nuclei with nucleases disrupts the fibrillar GP network and produce large globules (over 300 nm in diameter), evidently by fusion of the GP. In this case the nuclei lose DNA while retaining at least 70% of the histones. The diameter of the large globules depends on the concentration of PA. The GP apparently form by aggregation of PA complexes with core histones of nucleosomes and other positively charged chromatin proteins at regularly spaced sites on the partially deproteinized chromatin.