SYNMIKRO, Loewe-Zentrum für Synthetische Mikrobiologie, Philipps-Universität Marburg, Marburg, Germany.
Fachbereich Chemie, Philipps-Universität Marburg, Marburg, Germany.
mSphere. 2020 Sep 9;5(5):e00817-20. doi: 10.1128/mSphere.00817-20.
Although DNA-compacting proteins have been extensively characterized , knowledge of their DNA binding dynamics is greatly lacking. We have employed single-molecule tracking to characterize the motion of the three major chromosome compaction factors in , Smc (tructural aintenance of hromosomes) 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 , avoiding clashes with RNA and DNA polymerases. All types of cells need to compact their chromosomes containing their genomic information several-thousand-fold in order to fit into the cell. In eukaryotes, histones achieve a major degree of compaction and bind very tightly to DNA such that they need to be actively removed to allow access of polymerases to the DNA. Bacteria have evolved a basic, highly dynamic system of DNA compaction, accommodating rapid adaptability to changes in environmental conditions. We show that the histone-like protein HBsu exchanges on DNA on a millisecond scale and moves through the entire nucleoid containing the genome as a slow-mobility fraction and a dynamic fraction, both having short dwell times. Thus, HBsu achieves compaction via short and transient DNA binding, thereby allowing rapid access of DNA replication or transcription factors to DNA. Topoisomerase gyrase and Smc show different interactions with DNA , displaying continuous loading or unloading from DNA, or using two fractions, one moving through the genome and one statically bound on a time scale of minutes, respectively, revealing three different modes of DNA compaction .
虽然 DNA 紧缩蛋白已被广泛研究，但对于它们与 DNA 结合的动力学知识却知之甚少。我们利用单分子跟踪技术，研究了三种主要的染色体紧缩因子在中的运动情况：SMC（染色体结构维持）蛋白、拓扑异构酶 DNA 拓扑异构酶和组蛋白样蛋白 HBsu。我们发现，这三种蛋白质与 DNA 的相互作用模式存在显著差异；SMC 蛋白显示出两种迁移分数，一种是静态的，另一种是通过染色体以受限的方式移动，而拓扑异构酶则作为一个单一的慢迁移分数运作，这表明所有拓扑异构酶分子都在催化活性地参与 DNA 结合。相反，细菌组蛋白样蛋白 HBsu 作为一个较大的慢迁移分数和一个较小的高迁移分数穿过核质体移动，这两个分数的停留时间都相对较短。组成静态分数的 SMC 复合物的周转率对于其在染色体紧缩中的功能是重要的。我们的报告揭示了细菌中的染色体紧缩可以通过快速、短暂的相互作用发生，从而避免与 RNA 和 DNA 聚合酶发生冲突。所有类型的细胞都需要将包含其基因组信息的染色体压缩几千倍，以便容纳在细胞内。在真核生物中，组蛋白实现了主要程度的紧缩，并与 DNA 紧密结合，因此需要主动去除它们，以允许聚合酶进入 DNA。细菌已经进化出一种基本的、高度动态的 DNA 紧缩系统，以适应环境条件的快速变化。我们发现组蛋白样蛋白 HBsu 在毫秒尺度上在 DNA 上交换，并作为慢迁移分数和动态分数穿过包含基因组的整个核质体移动，两者的停留时间都很短。因此，HBsu 通过短暂和瞬时的 DNA 结合实现紧缩，从而允许 DNA 复制或转录因子快速进入 DNA。拓扑异构酶拓扑异构酶和 SMC 与 DNA 显示出不同的相互作用，分别表现为连续加载或卸载 DNA，或使用两个分数，一个通过基因组移动，一个在几分钟的时间尺度上静态结合，揭示了三种不同的 DNA 紧缩模式。
