Centre de Biochimie Structurale, CNRS UMR 5048, INSERM U1054, Université de Montpellier, 60 rue de Navacelles, 34090 Montpellier, France.
Laboratoire Charles Coulomb (L2C), Université de Montpellier, CNRS, Montpellier, France.
Mol Cell. 2020 Jul 16;79(2):293-303.e4. doi: 10.1016/j.molcel.2020.06.034.
Liquid-liquid phase-separated (LLPS) states are key to compartmentalizing components in the absence of membranes; however, it is unclear whether LLPS condensates are actively and specifically organized in the subcellular space and by which mechanisms. Here, we address this question by focusing on the ParABS DNA segregation system, composed of a centromeric-like sequence (parS), a DNA-binding protein (ParB), and a motor (ParA). We show that parS and ParB associate to form nanometer-sized, round condensates. ParB molecules diffuse rapidly within the nucleoid volume but display confined motions when trapped inside ParB condensates. Single ParB molecules are able to rapidly diffuse between different condensates, and nucleation is strongly favored by parS. Notably, the ParA motor is required to prevent the fusion of ParB condensates. These results describe a novel active mechanism that splits, segregates, and localizes non-canonical LLPS condensates in the subcellular space.
液-液相分离（LLPS）状态是在没有膜的情况下分隔成分的关键；然而，目前尚不清楚 LLPS 凝聚物是否在亚细胞空间中被主动且特异性地组织，以及通过哪些机制。在这里，我们通过关注 ParABS DNA 分离系统来解决这个问题，该系统由一个类似于着丝粒的序列（parS）、一个 DNA 结合蛋白（ParB）和一个马达（ParA）组成。我们表明，parS 和 ParB 结合形成纳米级的圆形凝聚物。ParB 分子在核质体积内快速扩散，但在被囚禁在 ParB 凝聚物内时表现出受限的运动。单个 ParB 分子能够在不同的凝聚物之间快速扩散，而且 parS 强烈促进成核。值得注意的是，ParA 马达是防止 ParB 凝聚物融合所必需的。这些结果描述了一种新的主动机制，该机制可将非典型的 LLPS 凝聚物在亚细胞空间中分裂、分离和定位。
