The tripartite ParABS system mediates chromosome segregation in the majority of bacterial species. Typically, DNA-bound ParB proteins around the parS sites condense the chromosomal DNA into a higher-order multimeric nucleoprotein complex for the ParA-driven partition. Despite extensive studies, the molecular mechanism underlying the dynamic assembly of the partition complex remains unclear. Herein, we demonstrate that Bacillus subtilis ParB (Spo0J), through the multimerization of its N-terminal domain, forms phase-separated condensates along a single DNA molecule, leading to the concurrent organization of DNA into a compact structure. Specifically, in addition to the co-condensation of ParB dimers with DNA, the engagement of well-established ParB condensates with DNA allows for the compression of adjacent DNA and the looping of distant DNA. Notably, the presence of CTP promotes the formation of condensates by a low amount of ParB at parS sites, triggering two-step DNA condensation. Remarkably, parS-centered ParB-DNA co-condensate constitutes a robust nucleoprotein architecture capable of withstanding disruptive forces of tens of piconewton. Overall, our findings unveil diverse modes of DNA compaction enabled by phase-separated ParB and offer new insights into the dynamic assembly and maintenance of the bacterial partition complex.

中文翻译：

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相分离的 ParB 强制执行多种 DNA 压缩模式并稳定以 parS 为中心的分区复合物


三方 ParABS 系统介导大多数细菌物种的染色体分离。通常，parS 位点周围的 DNA 结合 ParB 蛋白将染色体 DNA 浓缩成高阶多聚核蛋白复合物，用于 ParA 驱动的分区。尽管进行了大量研究，但分区复合物动态组装的分子机制仍不清楚。在此，我们证明枯草芽孢杆菌 ParB (Spo0J) 通过其 N 端结构域的多聚化，沿着单个 DNA 分子形成相分离的缩合物，从而导致 DNA 同时组织成紧凑的结构。具体来说，除了 ParB 二聚体与 DNA 的共缩合之外，成熟的 ParB 缩合物与 DNA 的接合还可以压缩邻近的 DNA 和使远处的 DNA 形成环。值得注意的是，CTP 的存在促进了少量 ParB 在 parS 位点形成缩合物，从而引发两步 DNA 缩合。值得注意的是，以 parS 为中心的 ParB-DNA 共缩合物构成了坚固的核蛋白结构，能够承受数十皮牛顿的破坏力。总的来说，我们的研究结果揭示了相分离 ParB 实现的多种 DNA 压缩模式，并为细菌分区复合物的动态组装和维护提供了新的见解。