Escherichia coli DNA ligase B may mitigate damage from oxidative stress

Escherichia coli encodes two DNA ligases, ligase A, which is essential under normal laboratory growth conditions, and ligase B, which is not. Here we report potential functions of ligase B. We found that across the entire Enterobacteriaceae family, ligase B is highly conserved in both amino acid identity and synteny with genes associated with oxidative stress. Deletion of ligB sensitized E. coli to specific DNA damaging agents and antibiotics resulted in a weak mutator phenotype, and decreased biofilm formation. Overexpression of ligB caused a dramatic extension of lag phase that eventually resumed normal growth. The ligase function of ligase B was not required to mediate the extended lag phase, as overexpression of a ligase-deficient ligB mutant also blocked growth. Overexpression of ligB during logarithmic growth caused an immediate block of cell growth and DNA replication, and death of about half of cells. These data support a potential role for ligase B in the base excision repair pathway or the mismatch repair pathway.大肠杆菌（Escherichia coli）编码两种DNA连接酶（DNA ligase）：连接酶A（ligase A）在常规实验室培养条件下为必需基因，而连接酶B（ligase B）则非必需。本研究报道了连接酶B的潜在功能。我们发现，在整个肠杆菌科（Enterobacteriaceae）类群中，连接酶B在氨基酸一致性以及与氧化应激相关基因的共线性层面均呈现高度保守性。删除ligB基因会使大肠杆菌对特定DNA损伤剂与抗生素敏感，同时引发较弱的突变体表型，并降低生物膜形成能力。过表达ligB会导致迟滞期显著延长，最终恢复正常生长。连接酶B的连接酶活性并非介导迟滞期延长所必需，因为过表达缺乏连接酶活性的ligB突变体同样可阻滞细胞生长。在对数生长期过表达ligB会立即阻断细胞生长与DNA复制，并导致约半数细胞死亡。上述实验数据支持连接酶B在碱基切除修复通路（base excision repair pathway）或错配修复通路（mismatch repair pathway）中发挥潜在作用。