Stretching of single collapsed DNA molecules
Stretching of single collapsed DNA molecules
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DOI：
10.1016/s0006-3495(00)76744-0
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发表时间：
2000-04-01
影响因子：
3.4
通讯作者：
Block, SM
中科院分区：
文献类型：
--
作者：
Baumann, CG;Bloomfield, VA;Block, SM
使用光镊在引起 DNA 大量凝聚的三价阳离子浓度下探测单个质粒和 λ 噬菌体 DNA 分子的弹性响应。对于未缩合的质粒，持久长度 P 随着亚精胺浓度的增加而减小，然后达到极限值 40 nm。当浓缩质粒被拉伸时，观察到两种类型的行为：棒释放模式和类似于 20 pN 的平台。这些行为归因于从压缩结构（例如卷曲 DNA）中解包。类似地，六氨合钴 (III) (CoHex) 和亚精胺的浓缩浓度会引起 lambda DNA 的丝束和高力弹性的广泛变化。高力（5-15 pN）熵弹性表现出蠕虫状链（WLC）行为，P 比低单价盐低两到五倍。在较低的力下，突然出现 14 pN 的平台。这对应于 0.083-0.33 kT/bp 的分子内吸引力，与大量浓缩 DNA 中的渗透应力测量结果一致。 CoHex 的分子内吸引力比亚精胺大，这与 CoHex 大量浓缩 DNA 的效率更高是一致的。从 WLC 行为到凝结的转变发生在轮廓长度约 85% 的延伸处，允许凝结成环和成核。当 CoHex 为缩合剂时，在拉伸链中成核塌陷所需的碱基对数量大约为一半。
The elastic response of single plasmid and lambda phage DNA molecules was probed using optical tweezers at concentrations of trivalent cations that provoked DNA condensation in bulk. For uncondensed plasmids, the persistence length, P, decreased with increasing spermidine concentration before reaching a limiting value 40 nm. When condensed plasmids were stretched, two types of behavior were observed: a stick-release pattern and a plateau at similar to 20 pN. These behaviors are attributed to unpacking from a condensed structure, such as coiled DNA. Similarly, condensing concentrations of hexaammine cobalt(III) (CoHex) and spermidine induced extensive changes in the tow and high force elasticity of lambda DNA. The high force (5-15 pN) entropic elasticity showed worm-like chain (WLC) behavior, with P two- to fivefold lower than in low monovalent salt. At lower forces, a 14-pN plateau abruptly appeared. This corresponds to an intramolecular attraction of 0.083-0.33 kT/bp, consistent with osmotic stress measurements in bulk condensed DNA. The intramolecular attractive force with CoHex is larger than with spermidine, consistent with the greater efficiency with which CoHex condenses DNA in bulk. The transition from WLC behavior to condensation occurs at an extension about 85% of the contour length, permitting looping and nucleation of condensation. Approximately half as many base pairs are required to nucleate collapse in a stretched chain when CoHex is the condensing agent.