School of Life Science and Technology, ShanghaiTech University, Shanghai, China.
Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, Shanghai, China.
Elife. 2020 Feb 26;9:e54098. doi: 10.7554/eLife.54098.
BLM is a multifunctional helicase that plays critical roles in maintaining genome stability. It processes distinct DNA substrates, but not nicked DNA, during many steps in DNA replication and repair. However, how BLM prepares itself for diverse functions remains elusive. Here, using a combined single-molecule approach, we find that a high abundance of BLMs can indeed unidirectionally unwind dsDNA from a nick when an external destabilizing force is applied. Strikingly, human replication protein A (hRPA) not only ensures that limited quantities of BLMs processively unwind nicked dsDNA under a reduced force but also permits the translocation of BLMs on both intact and nicked ssDNAs, resulting in a bidirectional unwinding mode. This activation necessitates BLM targeting on the nick and the presence of free hRPAs in solution whereas direct interactions between them are dispensable. Our findings present novel DNA unwinding activities of BLM that potentially facilitate its function switching in DNA repair.
BLM 是一种多功能解旋酶，在维持基因组稳定性方面发挥着关键作用。它在 DNA 复制和修复的许多步骤中处理不同的 DNA 底物，但不处理缺口 DNA。然而，BLM 如何为各种功能做好准备仍然难以捉摸。在这里，我们使用一种组合的单分子方法发现，当施加外部去稳定力时，大量的 BLM 确实可以从缺口处单向解开 dsDNA。引人注目的是，人类复制蛋白 A（hRPA）不仅确保有限数量的 BLM 在较低的力下进行性地解开缺口 dsDNA，而且还允许 BLM 在完整和缺口 ssDNA 上迁移，从而产生双向解开模式。这种激活需要 BLM 在缺口上的靶向定位和溶液中游离 hRPA 的存在，而它们之间的直接相互作用是可有可无的。我们的发现提出了 BLM 的新的 DNA 解旋活性，这可能有助于其在 DNA 修复中的功能转换。
