Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, NE 68198-6025, USA.
Int J Mol Sci. 2022 Aug 3;23(15):8613. doi: 10.3390/ijms23158613.
The rescue of stalled DNA replication forks is essential for cell viability. Impeded but still intact forks can be rescued by atypical DNA helicases in a reaction known as fork regression. This reaction has been studied at the single-molecule level using the DNA helicase RecG and, separately, using the eukaryotic SMARCAL1 enzyme. Both nanomachines possess the necessary activities to regress forks: they simultaneously couple DNA unwinding to duplex rewinding and the displacement of bound proteins. Furthermore, they can regress a fork into a Holliday junction structure, the central intermediate of many fork regression models. However, there are key differences between these two enzymes. RecG is monomeric and unidirectional, catalyzing an efficient and processive fork regression reaction and, in the process, generating a significant amount of force that is used to displace the tightly-bound SSB protein. In contrast, the inefficient SMARCAL1 is not unidirectional, displays limited processivity, and likely uses fork rewinding to facilitate RPA displacement. Like many other eukaryotic enzymes, SMARCAL1 may require additional factors and/or post-translational modifications to enhance its catalytic activity, whereas RecG can drive fork regression on its own.
停滞的 DNA 复制叉的拯救对于细胞存活至关重要。受阻但仍完整的叉可以通过非典型 DNA 解旋酶在称为叉回归的反应中被拯救。该反应已经在使用 DNA 解旋酶 RecG 的单分子水平上进行了研究，并且分别使用真核 SMARCAL1 酶进行了研究。这两种纳米机器都具有回归叉的必要活性：它们同时将 DNA 解旋与双链重绕以及结合蛋白的位移偶联。此外，它们可以将叉回归为 Holiday 连接结构，这是许多叉回归模型的中心中间产物。然而，这两种酶之间存在关键差异。RecG 是单体且单向的，催化有效的和连续的叉回归反应，并且在此过程中产生大量用于置换紧密结合的 SSB 蛋白的力。相比之下，低效的 SMARCAL1 不是单向的，显示出有限的连续性，并且可能使用叉重绕来促进 RPA 置换。像许多其他真核酶一样，SMARCAL1 可能需要额外的因素和/或翻译后修饰来增强其催化活性，而 RecG 可以自行驱动叉回归。
