Functions of bacterial type IA topoisomerases in the prevention of R-loop-dependent and -independent genomic instability.

细菌细胞生命的关键步骤是分裂产生两个相同的子细胞。这一事件使其代代相传。然而，在细胞分裂之前必须忠实完成的一个关键事件是将复制的遗传物质（染色体）分离到细胞的每一端，同时保持基因组的稳定性，以便每个子细胞可以在分裂后接受一条染色体。有了来自母细胞的全套基因，每个子细胞将能够生长和分裂。由于DNA的双螺旋性质，DNA链的缠结在复制过程中不可避免地发生。如果不适当和迅速地去除，这些缠绕将最终阻止复制复合物的进展，因此，将发生DNA损伤，染色体分离将是不可能的。DNA拓扑异构酶（topos）通过切割DNA并通过允许链通过和重新连接来解决与复制复合物的进展相关的拓扑问题。IA型拓扑异构酶以ssDNA为底物，是唯一普遍存在的拓扑异构酶，其中许多具有RNA拓扑异构酶活性。最后两个独特的特征强烈支持1A型拓扑结构在进化的早期就存在的假设，即，至少在最后一个普遍共同祖先（LUCA）中，可能在RNA世界中。IA型拓扑异构酶已被证明在超螺旋调节和基因组维持中发挥重要作用。我们最近的研究结果表明，来自模式生物大肠杆菌的1A型酶通过抑制R环的形成来维持基因组的稳定性，R环的形成通过尚未充分表征的机制威胁基因组的稳定性。此外，我们还发现了IA型拓扑结构和核苷酸切除DNA修复途径蛋白之间的遗传相互作用。我们未来五年研究的主要目标是描述E。coli IA型topos作用于基因组以维持其稳定性。为了实现我们的目标，我们将使用经典的细菌和分子遗传学以及最先进的单细胞和全基因组方法。我们研究计划的最终目标是了解DNA拓扑结构如何影响基因组稳定性，以及如何通过拓扑结构进行适当调节，以使遗传物质能够忠实地传递给子细胞。

A key step in the life of a bacterial cell is its division to generate two identical daughter cells. This event allows its perpetuation from generation to generation. However, one key event that must be faithfully accomplish before cell division, is the segregation of the replicated genetic material (chromosomes) to each end of the cell while maintaining the stability of the genome, so that each daughter cell can receive one chromosome following division. With a full set of the genes from the mother cell, each daughter cell will be able to grow and divide. Because of the double-helical nature of the DNA, entanglement of the DNA strands inevitably occurs during replication. If not properly and rapidly removed, these intertwines will eventually block the progression of the replication complex and, as a consequence, DNA damages will occur and chromosome segregation will not be possible. DNA topoisomerases (topos), by cutting DNA and by allowing strand passage and re-ligation solve the topological problem associated with the progression of replication complexes. Type IA topos use ssDNA as substrates, they are the sole ubiquitous topos and many of them possess RNA topo activity. The last two unique features strongly support the hypothesis that type 1A topos were present very early in evolution, i.e., at least in the last universal common ancestor (LUCA) and possibly in the RNA world. Type IA topoisomerases have been shown to play major roles in supercoiling regulation and genome maintenance. Our recent results indicate that type 1A enzymes from the model organism Escherichia coli, maintain the stability of the genome by inhibiting the formation of R-loops, which threaten the stability of the genome by mechanism(s) that are not well characterized. Moreover, we have uncovered a genetic interaction between type IA topos and proteins of the nucleotide excision DNA repair pathway. The main goal of our research over the next five years is to characterize the precise mechanisms by which E. coli type IA topos act on the genome to maintain its stability. To achieve our objective, we will use classical bacterial and molecular genetics as well as state-of-the-art single-cell and genome-wide approaches. The ultimate goal of our research program is to understand how DNA topology affects genome stability and how it is properly regulated by topos, to allow the faithful transmission of the genetic material to daughter cells.