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871.
If chromatin from chicken erythrocytes is enzymatically degraded in the presence of histone H5, nucleosomal DNA usually exceeds the size of 140 base pairs. Conditions are derived allowing the isolation of a 180 base pair particle which is subsequently characterized by histone binding and thermal denaturation studies. Association of H5 to such a particle is cooperative and occurs with a larger affinity than binding to specimens in the range of 140– 170 base pairs. Thermal denaduration studies show that some of the extra DNA participates in the main transition at 74°C (1 mm Na-cacodylate) indicating a tight binding to the histone core. Another part of the extra segment is loosely associated with the core but also distinct from free DNA. 相似文献
872.
873.
The kinetics of thiol modification of histone H3 from chicken erythrocyte nuclei with the fluorogenic compound N-[p-(2-benzimidazolyl)phenyl]maleimide was determined at pH 5.5 and 2°C. Comparative experiments were performed with H3 in the natural mixture of the other histones (whole histone), assembled in the nucleosomal and in H2a/H2b depleted core particles. Exposure of the H3 thiols in core particles occurs within a rather narrow NaCl concentration range. The transition midpoint is shifted to lower ionic strength with decreasing core particle concentration and with increasing concentration of ethidium bromide added. The results presented permit the following conclusions about the disassembly process of core particles. Release of the H2a/H2b pairs at 0.5–0.7 m NaCl is not directly correlated with an exposure of H3 thiols. Exposure occurs at around 0.1 m NaCl and starts with a rather fast conformational transition of the depleted core followed by histone-DNA dissociation. Comparative experiments exploring the air mediated oxidation of thiols and the reactivity of lysine side chains with fluorescamine illustrate that the thiol exposure is a rather distinct event in core particle disassembly. 相似文献
874.