Chromosome Dynamics in Bacillus Subtills

复制的染色体压缩和分解成形态和空间上不同的姐妹染色体 染色单体对于所有生物体中DNA的可靠分离至关重要，但是 对这些过程的基本原理知之甚少。在细菌中，染色体分离主要是由 DNA压缩，这被认为是通过染色体沿沿着DNA有序折叠而发生的 姐妹篇们互相吸引，彼此远离。在几乎所有的生物体中， 染色体结构维持（SMC）凝聚素复合物在这一过程中起着核心作用， 这些环状ATP酶如何起作用仍不清楚。 在枯草芽孢杆菌中，缩合素环在拓扑学上装载到邻近于 通过结合到着丝粒parS位点的分配蛋白ParB进行复制。利用染色体构象 捕获（Hi-C）和ChIP-seq，我们发现这些复合物然后向左和向右移动， 染色体臂一直延伸到末端，同时将两个臂拴在一起。我们的研究结果支持了 SMC复合物通过促增殖作用沿沿着DNA片段起作用的一个可推广的模型 DNA循环在这个模型中，这些环状复合物环绕着DNA侧翼的装载位点， 双链体在一起。当这些系绳离开它们的装载位置时，它们产生环。循环- 形成确保了这些复合物沿着相邻的DNA片段起作用， 纠缠在一起的姐妹染色体在B。枯草，进行性袢扩大集中于起始近端parS位点 把姐妹的起源吸引到自己身上，远离彼此。沿染色体的从头成环沿着 真核生物中的臂也可以解释凝聚素复合物如何压缩和分解姐妹染色单体， 有丝分裂，并提供了一种机制，形成转录绝缘结构域（也称为 拓扑相关结构域或TADs）。我们的研究 B。subtilis SMC复合体的研究强调了使用简单模型系统研究保守细胞的重要性 生物过程。本提案中描述的实验建立在我们最近的发现基础上， 初步发现，以确定这些广泛保守的复合物如何产生DNA环;这些环- 当它们到达复制末端时，形系链被移除; 在复制分离周期中重塑细菌染色体。

Compaction and resolution of replicated chromosomes into morphologically and spatially distinct sister chromatids is essential for faithful DNA segregation in all organisms, but the molecular mechanisms that underlie these processes are poorly understood. In bacteria, chromosome segregation is largely driven by DNA compaction, which is thought to occur by the orderly folding of chromosomes along adjacent DNA segments drawing replicated sisters in on themselves and away from each other. In virtually all organisms, Structural Maintenance of Chromosomes (SMC) condensin complexes play a central role in this process but how these ring-shaped ATPase function has remained unclear. In Bacillus subtilis, condensin rings are topologically loaded onto the chromosome adjacent to the origin of replication by the partitioning protein ParB bound to centromeric parS sites. Using chromosome conformation capture (Hi-C) and ChIP-seq, we discovered that these complexes then travel down the left and right chromosome arms all the way to the terminus while tethering the two arms together. Our findings support a generalizable model in which SMC complexes act along adjacent DNA segments by processively enlarging DNA loops. In this model, these ring-shaped complexes encircle the DNA flanking their loading site, tethering the duplexes together. As these tethers move away from their loading sites they generate loops. Loop- formation ensures that these complexes act along adjacent DNA segments and therefore resolve rather than tangle sister chromosomes. In B. subtilis, processive loop enlargement centered on origin-proximal parS sites draws sister origins in on themselves and away from each other. De novo loop formation along chromosome arms in eukaryotes can also explain how condensin complexes compact and resolve sister chromatids during mitosis and provides a mechanism for the formation of transcriptionally insulated domains (also called topologically associated domains or TADs) by SMC cohesin complexes during interphase. Our studies on the B. subtilis SMC complex highlights the importance of using simple model systems to study conserved cell biological processes. The experiments described in this proposal build on our recent discoveries and preliminary findings to define how these broadly conserved complexes generate DNA loops; how these ring- shaped tethers are removed when they reach the replication terminus; and the role of condensin in remodeling the bacterial chromosome during the replication-segregation cycle.