College of Life Sciences, Northwest A&F University, Yangling, Shaanxi, China.
Univ Lyon, ENS de Lyon, Univ Claude Bernard, CNRS UMR 5239, INSERM U1210, LBMC, Lyon, France.
FEBS J. 2017 Dec;284(23):4051-4065. doi: 10.1111/febs.14290. Epub 2017 Nov 8.
Non-canonical four-stranded G-quadruplex (G4) DNA structures can form in G-rich sequences that are widely distributed throughout the genome. The presence of G4 structures can impair DNA replication by hindering the progress of replicative polymerases (Pols), and failure to resolve these structures can lead to genetic instability. In the present study, we combined different approaches to address the question of whether and how Escherichia coli Pol I resolves G4 obstacles during DNA replication and/or repair. We found that E. coli Pol I-catalyzed DNA synthesis could be arrested by G4 structures at low protein concentrations and the degree of inhibition was strongly dependent on the stability of the G4 structures. Interestingly, at high protein concentrations, E. coli Pol I was able to overcome some kinds of G4 obstacles without the involvement of other molecules and could achieve complete replication of G4 DNA. Mechanistic studies suggested that multiple Pol I proteins might be implicated in G4 unfolding, and the disruption of G4 structures requires energy derived from dNTP hydrolysis. The present work not only reveals an unrealized function of E. coli Pol I, but also presents a possible mechanism by which G4 structures can be resolved during DNA replication and/or repair in E. coli.
非经典的四链构象 G-四链体（G4）DNA 结构可以在富含 G 的序列中形成，这些序列广泛分布于整个基因组中。G4 结构的存在会通过阻碍复制聚合酶（Pols）的前进而阻碍 DNA 复制，如果不能解决这些结构，就会导致遗传不稳定性。在本研究中，我们结合了不同的方法来解决大肠杆菌 Pol I 在 DNA 复制和/或修复过程中是否以及如何解决 G4 障碍的问题。我们发现，大肠杆菌 Pol I 催化的 DNA 合成可以在低蛋白浓度下被 G4 结构所抑制，并且抑制的程度强烈依赖于 G4 结构的稳定性。有趣的是，在高蛋白浓度下，大肠杆菌 Pol I 能够在不涉及其他分子的情况下克服某些类型的 G4 障碍，并能够实现 G4 DNA 的完全复制。机制研究表明，可能涉及多个 Pol I 蛋白来解旋 G4 结构，并且破坏 G4 结构需要来自 dNTP 水解的能量。本研究不仅揭示了大肠杆菌 Pol I 的一个未被认识的功能，而且还提出了一种可能的机制，即 G4 结构可以在大肠杆菌的 DNA 复制和/或修复过程中被解决。
