Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands.
School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.
Sci Adv. 2022 Jul;8(26):eabn3299. doi: 10.1126/sciadv.abn3299. Epub 2022 Jun 29.
The ParAB system is essential for prokaryotic chromosome segregation. After loading at on the genome, ParB (partition protein B) proteins rapidly redistribute to distances of ~15 kilobases from the loading site. It has remained puzzling how this large-distance spreading can occur along DNA loaded with hundreds of proteins. Using in vitro single-molecule fluorescence imaging, we show that ParB from can load onto DNA distantly of , as loaded ParB molecules themselves are found to be able to recruit additional ParB proteins from bulk. Notably, this recruitment can occur in cis but also in trans, where, at low tensions within the DNA, newly recruited ParB can bypass roadblocks as it gets loaded to spatially proximal but genomically distant DNA regions. The data are supported by molecular dynamics simulations, which show that cooperative ParB-ParB recruitment can enhance spreading. -independent recruitment explains how ParB can cover substantial genomic distance during chromosome segregation, which is vital for the bacterial cell cycle.
ParAB 系统对于原核染色体的分离至关重要。在基因组上的 处加载后，ParB（分区蛋白 B）蛋白迅速重新分布到距加载位点约 15 千碱基的距离。一直令人费解的是，如何沿着加载有数百种蛋白质的 DNA 进行这种远距离的扩散。我们使用体外单分子荧光成像技术表明，来自 的 ParB 可以加载到 DNA 上的远距离，因为已加载的 ParB 分子本身就能够从主体中招募额外的 ParB 蛋白。值得注意的是，这种招募可以发生在顺式，也可以发生在反式，在 DNA 中的张力较低时，新招募的 ParB 可以绕过障碍物，因为它加载到空间上接近但基因组上距离较远的 DNA 区域。这些数据得到了分子动力学模拟的支持，该模拟表明，协同 ParB-ParB 招募可以增强扩散。独立于 的招募解释了 ParB 如何在染色体分离过程中覆盖大量基因组距离，这对于细菌细胞周期至关重要。
