Neutron scattering studies of nucleosome structure at low ionic strength.
Neutron scattering studies of nucleosome structure at low ionic strength.
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低离子强度下核小体结构的中子散射研究。
DOI：
10.1021/bi00290a007
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发表时间：
1983
期刊：
影响因子：
2.9
通讯作者：
Bunick,GJ
中科院分区：
文献类型：
--
作者：
Uberbacher,EC;Ramakrishnan,V;Olins,DE;Bunick,GJ
摘要：用均相预EPA对含有146或175碱基对DNA的鸡红细胞核小体进行的离子强度研究表明，由小角中子散射确定的一次展开跃迁的离子强度约为1.5 mm。在两种类型的核小体粒子中，小角中子散射都没有观察到一些研究人员在2.9到7.5毫米离子强度之间看到的转变。测量的两个对比(H20和D20)表明，蛋白质核心只发生了很小的构象变化，但DNA在过渡点以下部分展开。数据的帕特森倒置和模型的分析表明，两种类型的颗粒中的DNA都从末端解开，留下大约一圈超螺旋DNA结合到组蛋白核心上，其构象大致正常(紧密)。这两种粒子的展开机制似乎是相似的，而且都是在相同的离子强度下发生的。在这项研究中观察到的核小体的展开与DNA的扩展超螺旋模型明确地不一致，也与包含未折叠的组蛋白核心的模型不一致。核小体的结构和动力学性质是当前深入研究的主题。转录活性基因中DNA可及性的变化表明，结构变化会影响基因组特定片段的功能状态(WeIntraub&Groudine，1976)。核小体水平上染色质结构的局部变化很可能至少部分地调节了重要事件，如转录和复制。描述核小体展开能力的一种方法是检查它们对离子强度变化的反应。离子强度降低会导致核小体核心颗粒可逆展开，而不会丢失蛋白质。研究这种低盐转变的方法多种多样，包括流体动力学(Gordon等人，1978,1979；Harrington等人，1981)、荧光测量(Dieterich等人，1979；Eshaghour等人，1980；Libertini&Small，1982)、电子显微镜(Oudet等人，1977)、电光技术(Crothers等人，1978；Wu等人，1979；Schless inger等人，1982)和化学交联法(Martinson等人，1979)。已经形成了一种共识，即在具有146个碱基对(BP)1 DNA的核心粒子中，以及在具有较长DNA的粒子中，发生了一个以约1.5 mm离子强度为中心的相对复杂的转变(Schless inger等人，1982)。一些研究人员在由约140个碱基对组成的粒子(Gordon等人，1978年)和具有175个碱基对DNA的粒子(Schless inger等人，1982)中观察到了离子强度在3至7 mm之间的第二个转变。尽管对这些转变进行了广泛的研究，但对于展开的方式或机制、展开的程度、展开结构的柔性或刚性以及组蛋白在这一过程中的参与程度似乎几乎没有达成一致。来自荧光的证据
Edward C. Uberbacher, Venkatraman Ramakrishnan,* Donald E. Olins, and Gerard J. Bunick* abstract: Ionic strength studies using homogeneous prepa-rations of chicken erythrocyte nucleosomes containing either 146 or 175 base pairs of DNA show a single unfolding tran-sition at about 1.5 mM ionic strength as determined by small-angle neutron scattering. The transition seen by some investigators at between 2.9 and 7.5 mM ionic strength is not observed by small-angle neutron scattering in either type of nucleosome particle. The two contrasts measured (H20 and D20) indicate that only small conformational changes occur in the protein core, but the DNA is partially unfolded below the transition point. Patterson inversion of the data and analysis of models indicate that the DNA in both types of particle is unwinding from the ends, leaving about one turn of supercoiled DNA bound to the histone core in approximately its normal (compact) conformation. The mechanism of unfolding appears to be similar for both types of particles and in both cases occurs at the same ionic strength. The unfolding observed for nucleosomes in this study is in definite disagreement with extended superhelical models for the DNA and also disagrees with models incorporating an unfolded histone core. e structural and dynamical properties of nucleosomes are a current subject of intense investigation. Changes in DNA accessibility in transcriptionally active genes suggest that structural alterations affect the functional state of specific segments of the genome (Weintraub &Groudine, 1976). It is likely that important events such as transcription and rep-lication are regulated, at least in part, by local changes in chromatin structure on the level of the nucleosome. One way to characterize the ability of nucleosomes to unfold has been to examine their response to variations in ionic strength. Reduced ionic strength causes a reversible unfolding of nucleosome core particles without loss of proteins. This low-salt transition has been studied by a wide variety of methods including hydrodynamics (Gordon et al., 1978, 1979; Harrington, 1981), fluorescence measurements (Dieterich et al., 1979; Eshaghpour et al., 1980; Libertini & Small, 1982), electron microscopy (Oudet et al., 1977), electrooptical techniques (Crothers et al., 1978; Wu et al., 1979; Schlessinger et al., 1982), and chemical cross-linking (Martinson et al., 1979). A consensus has emerged that one relatively complex transition occurs centered at about 1.5 mM ionicstrength in core particles with 146 base pair (bp) 1 DNA and also in particles with longer length DNA (Schlessinger et al., 1982). A second transition at between 3 and 7 mM ionic strength has been observedby some investigators in particles consisting of about 140 base pairs (Gordon et al., 1978) and in particles with 175 base pair DNA (Schlessinger et al., 1982). Despite the extensive investigation of these transitions, there seems to be little agreement as to the mode or mechanism of unfolding, thedegree of unfolding, the flexibility or rigidity of the unfolded structure, and the extent to which thehistones are involved in theprocess. Evidence from fluorescence
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染色质亚基的构象变化。
DOI：
--
发表时间：
1978
影响因子：
11.1
作者：
V. C. Gordon;C. Knobler;D. Olins;V. Schumaker
通讯作者：
V. Schumaker
DOI：
--
发表时间：
1973
期刊：
Biochemical and Biophysical Research Communications - BBRC
影响因子：
--
作者：
D. Hewish;L. Burgoyne
通讯作者：
L. Burgoyne
染色质亚基构象转变的温度和 pH 依赖性。
影响因子：
14.9
作者：
V. C. Gordon;V. Schumaker;D. Olins;C. Knobler;J. Horwitz
通讯作者：
J. Horwitz
亚核小体的圆二色性和热变性研究及其与核小体结构的关系。
影响因子：
2.9
作者：
A. Mencke;R. Rill
通讯作者：
R. Rill
影响因子：
3.8
作者：
KRATKY, O
通讯作者：
KRATKY, O