Chromatin reconstitution on small DNA rings. II. DNA supercoiling on the nucleosome.
Chromatin reconstitution on small DNA rings. II. DNA supercoiling on the nucleosome.
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小 DNA 环上的染色质重建。
DOI：
10.1016/0022-2836(88)90239-2
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发表时间：
1988
影响因子：
5.6
通讯作者：
A. Prunell
中科院分区：
文献类型：
--
作者：
Y. Zivanovic;I. Goulet;B. Révet;M. Le Bret;A. Prunell
通过用在小 DNA 环上重建的拓扑异构酶 I 单核小体和双核小体松弛来研究核小体上的 DNA 超螺旋。除了连接差异为整数的 359 个碱基对 (bp) 环外，还使用了另外两个系列的具有小数差异的环，大小分别为 341 和 354 bp。发现在 359 bp 环上重构的单核小体松弛成单个单核小体形式。相比之下，341 bp 和 354 bp 单核小体松弛成两种形式的混合物，对应于两种相邻的拓扑异构体。观察到，在每个环系列内，这两种形式之间的比率实际上与用于重构的拓扑异构体的初始连接数无关，这表明每个分区都反映了平衡。与在没有组蛋白的情况下观察到的相同环的平衡进行比较表明，单个核小体的形成与 - 1.1(± 0.1) 转的连接数变化相关。相反，双核小体没有完全松弛，也没有达到平衡。然而，每个核小体相应的连接数变化估计与上图类似，与先前从含有大量核小体的环状染色质获得的文献数据一致。随后通过高分辨率电子显微镜和凝胶电泳研究了单核小体中的 DNA 结构。研究发现，上述连接数减少可归因于具有大的开放核小体外DNA环且围绕组蛋白核心的超螺旋不超过1.5圈的颗粒。构建了小环上核小体的理论模型，其中 DNA 的一部分缠绕在圆柱体上，另一部分可以自由地扭转和弯曲。当超螺旋中 DNA 的扭曲每圈在 10.5 至 10.65 bp 之间时，预测的连接数减少与实验数据最为一致，这表明核小体上的缠绕不会显着改变 DNA 的扭曲。基于对用旋转酶处理重构微型染色体时获得的最新数据的分析，还得出了与两转核小体相关的连接数减少的较低估计值。 1.6 圈的值设定了核小体 DNA 扭转每圈 10.44 bp 的下限，与上述估计一致。这些结果与最近发现的核小体 DNA 的 10.2 bp 序列周期之间存在差异的原因根据分别用于两种测量的不同参考系（绝对参考系和局部参考系）进行了讨论。
DNA supercoiling on the nucleosome was investigated by relaxing with topoisomerase I mono- and dinucleosomes reconstituted on small DNA rings. Besides 359 base-pair (bp) rings whose linking differences were integers, two additional series of rings with fractional differences, 341 and 354 bp in size, were used. Mononucleosomes reconstituted on 359 bp rings were found to relax into a single mononucleosome form. In contrast, 341 and 354 bp mononucleosomes relaxed into a mixture of two forms, corresponding to two adjacent topoisomers. The observation that the ratio between these two forms was, within each ring series, virtually independent of the initial linking number of the topoisomer used for the reconstitution suggested that each partition reflected an equilibrium. Comparison with the equilibria observed for the same rings in the absence of histones showed that the formation of a single nucleosome is associated with a linking number change of − 1.1(± 0.1) turn. Dinucleosomes, in contrast, were not relaxed to completion and do not reach equilibria. The corresponding linking number change per nucleosome was, however, estimated to be similar to the above figure, in agreement with previous data from the literature obtained with circular chromatins containing larger numbers of nucleosomes.DNA structure in mononucleosomes was subsequently investigated by means of high-resolution electron microscopy and gel electrophoresis. It was found that the above linking number reduction could be ascribed to a particle with a large open extranucleosomal DNA loop and with no more than 1.5 turns of a superhelix around the histone core. A theoretical model of a nucleosome on a small ring was constructed in which one part of the DNA was wrapped around a cylinder and the other part was free to vary both in torsion and flexion. The linking number reduction predicted was found to be most consistent with experimental data when the twist of the DNA in the superhelix was between 10.5 and 10.65 bp per turn, suggesting that wrapping on the nucleosome does not alter the twist of the DNA significantly. A lower estimate of the linking number reduction associated with a two-turn nucleosome was also derived, based on an analysis of recent data obtained upon treatment of reconstituted minichromosomes with gyrase. The value, 1.6 turns, set a lower limit of 10.44 bp per turn for the twist of nucleosomal DNA, in agreement with the above estimate. Reasons for the discrepancy between these results and the sequence periodicity of 10.2 bp recently found for nucleosomal DNA are discussed in terms of the different reference frames, absolute and local, respectively used for the two measurements.
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影响因子：
5.6
作者：
SHORE, D;BALDWIN, RL
通讯作者：
BALDWIN, RL
影响因子：
5.6
作者：
DREW, HR;TRAVERS, AA
通讯作者：
TRAVERS, AA
影响因子：
5.6
作者：
HOROWITZ, DS;WANG, JC
通讯作者：
WANG, JC
影响因子：
5.6
作者：
SATCHWELL, SC;DREW, HR;TRAVERS, AA
通讯作者：
TRAVERS, AA