单染色质纤维在正扭应力作用下的核小体手性转变
Nucleosome Chiral Transition under Positive Torsional Stress in Single Chromatin Fibers
摘要：
使用磁镊研究单个染色质纤维的机械响应，我们发现，纤维提交到大的正扭转瞬时陷阱正转，在一个转每核小体的速度。与通过耗尽H2 A-H2 B二聚体获得的四体（与~50 bp DNA结合的（H3-H4）2四聚体）纤维的反应进行比较，表明捕获反映了核小体手性转变为建立在先前记录的右手四体上的亚稳态形式。鉴于其低能量，<8 kT，我们提出这种转变是生理相关的，并用于打破二聚体在四聚体上的对接，在没有其他因素的情况下，四聚体对主要RNA聚合酶的转录延伸产生强烈的阻断。
英文摘要：
Using magnetic tweezers to investigate the mechanical response of single chromatin fibers, we show that fibers submitted to large positive torsion transiently trap positive turns, at a rate of one turn per nucleosome. A comparison with the response of fibers of tetrasomes (the (H3-H4)2 tetramer bound with ~50 bp of DNA) obtained by depletion of H2A-H2B dimers, suggests that the trapping reflects a nucleosome chiral transition to a metastable form built on the previously documented righthanded tetrasome. In view of its low energy, <8 kT, we propose this transition is physiologically relevant and serves to break the docking of the dimers on the tetramer which in the absence of other factors exerts a strong block against elongation of transcription by the main RNA polymerase.
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