Histone-histone interaction mediates chromatin unfolding at physiological ionic strength.
Histone-histone interaction mediates chromatin unfolding at physiological ionic strength.
复制标题
组蛋白-组蛋白相互作用介导染色质在生理离子强度下展开。
DOI：
10.1021/bi00440a013
复制
发表时间：
1989
期刊：
影响因子：
2.9
通讯作者：
Harrington,RE
中科院分区：
文献类型：
--
作者：
Riehm,MR;Harrington,RE
内华达州大学生物化学系，里诺，内华达州89557接收于1988年6月9日;修订的Mandarin pt接收于1989年3月22日摘要：据报道，鸡红细胞染色质的高分辨率热变性数据在NaCl浓度下超过4个数量级，包括生理区域。一种新的技术，使用临界点聚丙烯酰胺溶胶，而不是普通的溶剂，有效地稳定染色质沉淀在高盐浓度。这些溶胶是光学透明的，从260至320 nm，并在研究的温度范围内是热稳定的。在Na+离子浓度低于10 mM时，聚丙烯酰胺可能通过组蛋白HI和H5与羧酸残基的相互作用，在核小体水平上使染色质略微不稳定。在相同的低盐条件下，聚丙烯酰胺使纯DNA稳定，防止变性，大概是通过机械稳定它，防止螺旋扭曲的热波动。然而，在这两种情况下，聚丙烯酰胺溶胶在较高的盐下是完全非侵入性的。显着的低温热转变观察染色质在100 mM NaCl和以上whichevidently与DNA的构象变化。我们的结果与以下观点雅阁：在生理离子强度（100 mM Na+）下，组蛋白-组蛋白相互作用可能与组蛋白-DNA相互作用相当，因此在这些条件下可能足以促进染色质中DNA螺旋的不稳定。生物学的影响，这进行了讨论，并提出了一个可能的模型，在生理条件下的染色质的局部去凝聚。近年来，真核染色质的结构受到了相当大的关注，并且已经提出了从核小体到中期染色体水平的无活性染色质的超分子结构的合理模型[综述见纽波特和福布斯（1987）以及纳尔逊等人（1988）]。（1986）]。然而，导致转录、复制和DNA修复的激活和活性状态的解折叠途径尚未得到很好的理解[综述见Gross和Garrard（1988）和Weintraub（1985）]。在某种程度上，这是由于问题的内在复杂性，因为展开的染色质显然可以通过无数的亚稳态构象状态，与蛋白质的折叠和解折叠一样。此外，很少有实验技术能够解决这些状态的局部结构。由于盐和温度都影响染色质的稳定性，人们一直认为这些变量的组合可以导致结构状态，模仿那些与染色质活化。染色质浓缩与增加盐的阶段，这显然反映了核小体和纤维状的高级结构的层次。低于3 mM Na+的核小体构象转变的体外研究表明，侧翼DNA从核心展开，在中心核心留下大约一个DNA超螺旋环（Uberbacher et al.，1983;哈灵顿，1982，1981; Wu等人，1979年）。上述
Department of Biochemistry, University of Nevada, Reno, Nevada 89557 Received June 9, 1988; Revised Manuscript Received March 22, 1989 abstract: High-resolution thermal denaturation data on chicken erythrocyte chromatin are reported over 4 orders of magnitude in NaCl concentration which includes the physiological region. A novel technique using critical-point polyacrylamide sols instead of ordinary solvents effectively stabilizes chromatin against precipitation at high salt concentrations. These sols are optically transparent from 260 to 320 nm and are thermally stable over the temperature ranges studied. At Na+ ion concentrations below 10 mM, the polyacrylamide slightly destabilizes chromatin at thenucleosome level, possibly through interactions of histones HI and H5with the carboxylic acid residues. At the same low salts, polyacrylamide stabilizes pure DNA against denaturation, presumably by mechanically stabilizing it against helix-distorting thermal fluctuations. In both cases, however, the polyacrylamide sols are entirely noninvasiveat higher salts. Prominent low-temperature thermal transitions are observed in chromatin at and above 100 mM NaCl whichevidently are associated with conformational changes in DNA. Our results are in accord with the idea that histone-histone interactions at physiological ionic strengths—100 mM Na+) may be comparable to hi-stone-DNA interactions and hence may be sufficient to promote the destabilization of the DNA helix in chromatin under these conditions. The biological implications of this are discussed, and a possible model for the local decondensation of chromatin under physiological conditions is proposed. e structure of eukaryotic chromatin has received considerable attention in recent years, and reasonable models for the supramolecular architecture of inactive chromatin from the nucleosome to the metaphase chromosomal levels have been proposed [reviewed in Newport and Forbes (1987) and Nelson et al.(1986)]. However, unfolding pathways leading to ac-tivated and active states with respect to transcription, replication, and DNA repair are not well understood [reviewed in Gross and Garrard (1988) and Weintraub (1985)]. In part, this is due to the intrinsic complexity of the problem since unfolding chromatin can evidently pass through a myriad of metastable conformational states, as with the folding and unfolding of proteins. In addition, few experimentaltechniques are capable of resolving these states in terms of local structure. Since both salt and temperatureaffect chromatin stability, it has long been assumed that combinations of these variables can lead to structural states which mimic those associated with chromatin activation.Chromatin condenses with increasing salt in stages which evidently reflect the hierarchy of nucleosomal and fibrillar higher order structures. In vitro studies of the nucleosome conformational transition below 3 mM Na+ suggest that flanking DNA unfolds from the core, leaving approximately one superhelical loop of DNA at the central core (Uberbacher et al., 1983; Harrington, 1982, 1981; Wu et al., 1979). Above