Undritsov I M, Naktinis V I, Vengerov Iu Iu, Vashakidze R P, Karpenchuk K G
Mol Biol (Mosk). 1982 Jul-Aug;16(4):720-30.
The action of DNA topoisomerase I on the complexes of supercoiled DNA (DNA I) with histone H1 and other histones was studied at different ionic conditions and histone/DNA ratios. In the presence of 0.15 M NaCl at histone H1/DNA ratios lower than 0.25 (w/w) the relaxation of DNA I is not inhibited. Raising of H1/DNA I ratio up to 0.7 is followed by significant inhibition of DNA I relaxation. At fixed H1/DNA I ratio maximal inhibition is detected at 0.25 M NaCl. At NaCl concentrations lower than 0.1 M and higher than 0.3 M increasing of DNA I relaxation in the presence of H1 was observed. Electron microscopic studies show that increase of ionic strength or H1/DNA I ratio causes more dense packing of DNA molecules in the H1.DNA complexes. Changes in the structure of complexes agree with the increase of DNA I relaxation inhibition in these conditions. DNA I relaxation inhibition by H1 is drastically decreased by iodination of tyrosine 72 residue in the globular part of H1 molecule. Individual core histones inhibit DNA I relaxation at much higher histone/DNA ratios and show different dependence of inhibition on ionic strength. The results are discussed in terms of the possible role of H1 in chromatin condensation-decondensation.
在不同离子条件和组蛋白/DNA比例下，研究了DNA拓扑异构酶I对超螺旋DNA（DNA I）与组蛋白H1及其他组蛋白复合物的作用。在0.15M NaCl存在下，当组蛋白H1/DNA比例低于0.25（w/w）时，DNA I的松弛不受抑制。将H1/DNA I比例提高到0.7会导致DNA I松弛受到显著抑制。在固定的H1/DNA I比例下，在0.25M NaCl时检测到最大抑制作用。在NaCl浓度低于0.1M和高于0.3M时，观察到在H1存在下DNA I松弛增加。电子显微镜研究表明，离子强度或H1/DNA I比例的增加会导致H1-DNA复合物中DNA分子的堆积更紧密。复合物结构的变化与这些条件下DNA I松弛抑制的增加一致。通过对H1分子球状部分的酪氨酸72残基进行碘化，H1对DNA I松弛的抑制作用大幅降低。单个核心组蛋白在更高的组蛋白/DNA比例下抑制DNA I松弛，并且显示出不同的抑制对离子强度的依赖性。根据H1在染色质凝聚-解凝聚中的可能作用对结果进行了讨论。
