Chromosome organization mediated by structural maintenance of chromosomes (SMC) complexes is vital in many organisms. SMC complexes act as motors that extrude DNA loops, but it remains unclear what happens when multiple complexes encounter one another on the same DNA in living cells and how these interactions may help to organize an active genome. We therefore created a crash-course track system to study SMC complex encounters in vivo by engineering defined SMC loading sites in the Bacillus subtilis chromosome. Chromosome conformation capture (Hi-C) analyses of over 20 engineered strains show an amazing variety of chromosome folding patterns. Through three-dimensional polymer simulations and theory, we determine that these patterns require SMC complexes to bypass each other in vivo, as recently seen in an in vitro study. We posit that the bypassing activity enables SMC complexes to avoid traffic jams while spatially organizing the genome.

由染色体结构维持 (SMC) 复合物介导的染色体组织在许多生物体中至关重要。SMC 复合物充当了挤出 DNA 环的马达，但目前尚不清楚当多个复合物在活细胞中的同一 DNA 上相互相遇时会发生什么，以及这些相互作用如何有助于组织一个活跃的基因组。因此，我们创建了一个速成课程跟踪系统，通过在枯草芽孢杆菌中设计定义的 SMC 加载位点来研究体内 SMC 复合物的遭遇。染色体。对 20 多种工程菌株的染色体构象捕获 (Hi-C) 分析显示出惊人的多种染色体折叠模式。通过三维聚合物模拟和理论，我们确定这些模式需要 SMC 复合物在体内相互绕过，正如最近在体外研究中看到的那样。我们假设绕过活动使 SMC 复合体能够在空间组织基因组的同时避免交通拥堵。