Chromosome Dynamics in Bacillus Subtills

将复制的染色体压缩和拆分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忠实的DNA分离是必不可少的，但分子机制 这些过程背后的原因是人们对此知之甚少。在细菌中，染色体分离很大程度上是由 DNA紧凑，被认为是通过染色体沿着相邻的DNA有序折叠而发生的 片段将复制的姐妹吸引到自己身上，并相互远离。在几乎所有的有机体中， 染色体的结构维持(SMC)凝集素复合体在这一过程中发挥着核心作用，但 这些环形ATPase是如何发挥作用的，目前尚不清楚。 在枯草芽孢杆菌中，凝聚素环以拓扑方式加载到染色体上，靠近 通过与着丝粒PARS位点结合的分割蛋白PARB复制。利用染色体构象 捕获(Hi-C)和芯片序列，我们发现这些复合体随后向左和向右移动 染色体臂一直延伸到末端，同时将两条臂系在一起。我们的发现支持一种 SMC复合体通过连续放大沿相邻DNA片段作用的可推广模型 DNA循环。在这个模型中，这些环状复合体围绕着它们的装载部位两侧的dna，系住。 两个复式组合在一起。当这些系绳离开它们的装载位置时，它们会产生环路。循环- 形成确保这些复合体沿着相邻的DNA片段作用，从而分解而不是 缠绕在一起的姐妹染色体。在枯草芽孢杆菌中，以起源-近端部分为中心的进行性环扩大 把姐妹的血统吸引到自己身上，而不是彼此。沿染色体的从头环形成 真核生物中的手臂也可以解释凝集素复合体是如何压缩和分解姐妹染色单体的 有丝分裂，提供了一种形成转录绝缘结构域的机制(也称为 SMC粘附素复合体在相界面上的结构域(TAD)。我们对生物多样性的研究 枯草杆菌SMC复合体强调了用简单的模型系统研究保守细胞的重要性 生物过程。这项建议中描述的实验建立在我们最近的发现和 定义这些广泛保守的复合体如何产生DNA环的初步发现；这些环是如何- 当形状的系链到达复制末端时，它们被移除；凝聚在 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.