Centre for DNA Fingerprinting and Diagnosticsgrid.145749.a, Hyderabad, Telangana, India.
Graduate Studies, Manipal Academy of Higher Education, Manipal, Karnataka, India.
J Bacteriol. 2022 Apr 19;204(4):e0056921. doi: 10.1128/jb.00569-21. Epub 2022 Mar 28.
Homologous recombination (HR) is critically important for chromosomal replication, as well as DNA damage repair in all life forms. In Escherichia coli, the process of HR comprises (i) two parallel presynaptic pathways that are mediated, respectively, by proteins RecB/C/D and RecF/O/R/Q; (ii) a synaptic step mediated by RecA that leads to generation of Holliday junctions (HJs); and (iii) postsynaptic steps mediated sequentially by HJ-acting proteins RuvA/B/C followed by proteins PriA/B/C of replication restart. Combined loss of RuvA/B/C and a DNA helicase UvrD is synthetically lethal, which is attributed to toxicity caused by accumulated HJs since viability in these double mutant strains is restored by removal of the presynaptic or synaptic proteins RecF/O/R/Q or RecA, respectively. Here we show that, as in Δ strains, mutations confer synthetic lethality in cells deficient for transcription termination factor Rho, and that loss of RecFORQ presynaptic pathway proteins or of RecA suppresses this lethality. Furthermore, loss of IF2-1 (which is one of three isoforms [IF2-1, IF2-2, and IF2-3] of the essential translation initiation factor IF2 that are synthesized from three in-frame initiation codons in ) also suppressed and lethalities, whereas deficiency of IF2-2 and IF2-3 exacerbated the synthetic defects. Our results suggest that Rho deficiency is associated with an increased frequency of HR that is mediated by the RecFORQ pathway along with RecA. They also lend support to earlier reports that IF2 isoforms participate in DNA transactions, and we propose that they do so by modulation of HR functions. The process of homologous recombination (HR) is important for maintenance of genome integrity in all cells. In Escherichia coli, the RecA protein is a critical participant in HR, which acts at a step common to and downstream of two HR pathways mediated by the RecBCD and RecFOR proteins, respectively. In this study, an isoform (IF2-1) of the translation initiation factor IF2 has been identified as a novel facilitator of RecA's function during HR.
同源重组 (HR) 对于所有生命形式的染色体复制以及 DNA 损伤修复都至关重要。在大肠杆菌中，HR 过程包括：（i）由 RecB/C/D 和 RecF/O/R/Q 蛋白分别介导的两条平行的预突触途径；（ii）由 RecA 介导的突触步骤，导致形成 Holliday 连接（HJs）；和（iii）由 HJ 作用蛋白 RuvA/B/C 随后由复制起始蛋白 PriA/B/C 依次介导的后突触步骤。RuvA/B/C 和 DNA 解旋酶 UvrD 的联合缺失是合成致死的，这归因于由于 HJ 的积累而导致的毒性，因为这些双突变株的存活能力通过去除预突触或突触蛋白 RecF/O/R/Q 或 RecA 分别恢复。在这里，我们表明，与在Δ菌株中一样，突变赋予了转录终止因子 Rho 缺陷细胞的合成致死性，并且 RecFORQ 预突触途径蛋白或 RecA 的缺失抑制了这种致死性。此外，IF2-1 的缺失（它是从三个框架内起始密码子合成的三种必需翻译起始因子 IF2 的三个同工型 [IF2-1、IF2-2 和 IF2-3] 之一）也抑制了和的致死性，而 IF2-2 和 IF2-3 的缺乏则加剧了合成缺陷。我们的结果表明，Rho 缺陷与由 RecFORQ 途径以及 RecA 介导的 HR 频率增加有关。它们还支持了早期关于 IF2 同工型参与 DNA 交易的报道，并且我们提出它们通过调节 HR 功能来参与 DNA 交易。同源重组 (HR) 对于所有细胞中基因组完整性的维持都很重要。在大肠杆菌中，RecA 蛋白是 HR 的关键参与者，它作用于由 RecBCD 和 RecFOR 蛋白分别介导的两条 HR 途径的共同和下游步骤。在这项研究中，鉴定出翻译起始因子 IF2 的一种同工型（IF2-1）是 RecA 在 HR 过程中功能的新型促进因子。
