Laboratory of Molecular Biology, National Institute of Diabetes, and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0540, USA.
EMBO J. 2013 May 2;32(9):1238-49. doi: 10.1038/emboj.2013.34. Epub 2013 Feb 26.
DNA segregation ensures the stable inheritance of genetic material prior to cell division. Many bacterial chromosomes and low-copy plasmids, such as the plasmids P1 and F, employ a three-component system to partition replicated genomes: a partition site on the DNA target, typically called parS, a partition site binding protein, typically called ParB, and a Walker-type ATPase, typically called ParA, which also binds non-specific DNA. In vivo, the ParA family of ATPases forms dynamic patterns over the nucleoid, but how ATP-driven patterning is involved in partition is unknown. We reconstituted and visualized ParA-mediated plasmid partition inside a DNA-carpeted flowcell, which acts as an artificial nucleoid. ParA and ParB transiently bridged plasmid to the DNA carpet. ParB-stimulated ATP hydrolysis by ParA resulted in ParA disassembly from the bridging complex and from the surrounding DNA carpet, which led to plasmid detachment. Our results support a diffusion-ratchet model, where ParB on the plasmid chases and redistributes the ParA gradient on the nucleoid, which in turn mobilizes the plasmid.
DNA 分离确保了遗传物质在细胞分裂前的稳定遗传。许多细菌染色体和低拷贝质粒，如 P1 和 F 质粒，采用三组分系统来分配复制的基因组：DNA 靶标上的一个分区位点，通常称为 parS，一个分区位点结合蛋白，通常称为 ParB，和一个 Walker 型 ATP 酶，通常称为 ParA，它也结合非特异性 DNA。在体内，ParA 家族的 ATP 酶在核区形成动态模式，但 ATP 驱动的模式如何参与分区尚不清楚。我们在一个 DNA 覆盖的流动池中重建和可视化了 ParA 介导的质粒分区，该流动池充当人工核区。ParA 和 ParB 瞬时桥接质粒与 DNA 地毯。ParB 刺激 ParA 的 ATP 水解导致 ParA 从桥接复合物和周围的 DNA 地毯中解体，从而导致质粒脱落。我们的结果支持扩散棘轮模型，其中质粒上的 ParB 追踪并重新分配核区上的 ParA 梯度，这反过来又使质粒移动。
