Although DNA-compacting proteins have been extensively characterized in vitro, knowledge of their DNA binding dynamics in vivo is greatly lacking. We have employed single-molecule tracking to characterize the motion of the three major chromosome compaction factors in Bacillus subtilis, Smc (structural maintenance of chromosomes) proteins, topoisomerase DNA gyrase, and histone-like protein HBsu. We show that these three proteins display strikingly different patterns of interaction with DNA; while Smc displays two mobility fractions, one static and one moving through the chromosome in a constrained manner, gyrase operates as a single slow-mobility fraction, suggesting that all gyrase molecules are catalytically actively engaged in DNA binding. Conversely, bacterial histone-like protein HBsu moves through the nucleoid as a larger, slow-mobility fraction and a smaller, high-mobility fraction, with both fractions having relatively short dwell times. Turnover within the SMC complex that makes up the static fraction is shown to be important for its function in chromosome compaction. Our report reveals that chromosome compaction in bacteria can occur via fast, transient interactions in vivo, avoiding clashes with RNA and DNA polymerases.

中文翻译：

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枯草芽孢杆菌中的主要染色体凝聚因子 Smc、HBsu 和回旋酶通过截然不同的运动模式起作用。

尽管 DNA 压缩蛋白已在体外得到广泛表征，但对其体内DNA 结合动力学的了解却非常缺乏。我们已经采用单分子跟踪以表征在三大染色体压实因素的运动枯草芽孢杆菌，SMC（š tructural米的aintenance Çhromosomes) 蛋白质、拓扑异构酶 DNA 促旋酶和组蛋白样蛋白质 HBsu。我们表明这三种蛋白质与 DNA 的相互作用模式截然不同；虽然 Smc 显示出两种流动性部分，一种是静态的，一种是以受限方式通过染色体移动的，但回旋酶作为单一的慢速移动部分运行，这表明所有回旋酶分子都在催化上积极参与 DNA 结合。相反，细菌组蛋白样蛋白 HBsu 作为较大的慢移动部分和较小的高移动部分移动通过类核，这两个部分的停留时间相对较短。构成静态部分的 SMC 复合物内的周转对其在染色体压实中的功能很重要。我们的报告表明，细菌中的染色体压实可以通过快速、在体内，避免与 RNA 和 DNA 聚合酶发生冲突。