DNA-loop formation on nucleosomes shown by in situ scanning force microscopy of supercoiled DNA
DNA-loop formation on nucleosomes shown by in situ scanning force microscopy of supercoiled DNA
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DOI：
10.1016/j.jmb.2004.11.016
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发表时间：
2005-01-28
影响因子：
5.6
通讯作者：
Langowski, J
中科院分区：
文献类型：
--
作者：
Bussiek, M;Tóth, K;Langowski, J
染色质结构的灵活性是基因组DNA加工所必需的，它受许多因素控制，其中核小体的灵活性和移动性是必不可少的。在这里，DNA超螺旋对单个核小体结构的影响，进行了研究。用扫描力显微镜（SFM）在水溶液中观察用组蛋白亚饱和的环状超螺旋质粒DNA。与拓扑分析相比，SFM成像表明当盐浓度从10 mM升高至100 mM NaCl时核小体不稳定。在沉积到使用的扫描表面（即涂覆有聚赖氨酸的云母）后观察到核小体。在图像上，核小体以很高的概率出现在超螺旋顶端附近的末端环中。在100 mM NaCl中，但不是在10 mM NaCl中，大量的复合物存在于核小体中。在主要位于末端环附近的超螺旋交叉上。这些结构的形态学和统计分析表明，DNA环上形成的组蛋白八聚体，其中环的大小分布显示在50 nm处的一个明显的峰。最近，八聚体环的形成和扩散被认为是核小体沿着DNA易位的一种机制。所提供的数据可能证实了袢的发生，其可通过超螺旋稳定。对不位于交叉点上的规则核小体的结构的分析表明，降低盐浓度导致更多的构象，其中DNA从八聚体的远端部分解包。(C)2004爱思唯尔有限公司保留所有权利。
The flexibility of the chromatin structure, necessary for the processing of the genomic DNA, is controlled by a number of factors where flexibility and mobility of the nucleosomes is essential. Here, the influence of DNA supercoiling on the structure of single nucleosomes, is investigated. Circular supercoiled plasmid DNA sub-saturated with histones was visualized by scanning force microscopy (SFM) in aqueous solution. SFM-imaging compared with topological analysis indicates instability of nucleosomes when the salt concentration is raised from 10 mM to 100 mM NaCl. Nucleosomes were observed after the deposition to the used scanning surface, i.e. mica coated with polylysine. On the images, the nucleosomes, appear with a high probability in end-loops near the apices of the superhelices. In 100 mM NaCl but not in 10 mM NaCl, a significant number of complexes present the nucleosomes. on superhelical crossings mainly located adjacent to an end-loop. The morphology of these structures and statistical analysis suggest that DNA loops were formed on the histone octamers, where the loop size distribution shows a pronounced peak at 50 nm. Recently, the formation and diffusion of loops on octamers has been discussed as a mechanism of translocations of nucleosomes along DNA. The presented data likely confirm the occurrence of loops, which may be stabilized by supercoiling. Analysis of the structure of regular nucleosomes not located on crossings indicates that reducing the salt concentration leads to more conformations, where DNA is partially unwrapped from the distal ends of the octamer. (C) 2004 Elsevier Ltd. All rights reserved.