Institut Curie, Centre National de la Recherche Scientifique UMR 168, Université Pierre et Marie Curie, Paris, France.
Biophys J. 2011 Jun 8;100(11):2726-35. doi: 10.1016/j.bpj.2011.03.064.
Genomic DNA in eukaryotic cells is organized in supercoiled chromatin fibers, which undergo dynamic changes during such DNA metabolic processes as transcription or replication. Indeed, DNA-translocating enzymes like polymerases produce physical constraints in vivo. We used single-molecule micromanipulation by magnetic tweezers to study the response of chromatin to mechanical constraints in the same range as those encountered in vivo. We had previously shown that under positive torsional constraints, nucleosomes can undergo a reversible chiral transition toward a state of positive topology. We demonstrate here that chromatin fibers comprising linker histones present a torsional plasticity similar to that of naked nucleosome arrays. Chromatosomes can undergo a reversible chiral transition toward a state of positive torsion (reverse chromatosome) without loss of linker histones.
真核细胞中的基因组 DNA 组织在超螺旋染色质纤维中，在转录或复制等 DNA 代谢过程中经历动态变化。事实上，像聚合酶这样的 DNA 转运酶在体内产生物理限制。我们使用磁镊的单分子微操作来研究染色质对机械限制的反应，其范围与体内遇到的范围相同。我们之前已经表明，在正扭转约束下，核小体可以向具有正拓扑的状态发生可逆的手性转变。在这里，我们证明包含连接组蛋白的染色质纤维表现出与裸露核小体阵列相似的扭转塑性。染色质小体可以向正扭转（反向染色质小体）的状态发生可逆的手性转变，而不会丢失连接组蛋白。
