Division of Infectious Diseases, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
G3 (Bethesda). 2022 Feb 4;12(2). doi: 10.1093/g3journal/jkab409.
The bacterial DNA damage response pathway (SOS response) is composed of a network of genes regulated by a single transcriptional repressor, LexA. The lexA promoter, itself, contains two LexA operators, enabling negative feedback. In Escherichia coli, the downstream operator contains a conserved DNA cytosine methyltransferase (Dcm) site that is predicted to be methylated to 5-methylcytosine (5mC) specifically during stationary phase growth, suggesting a regulatory role for DNA methylation in the SOS response. To test this, we quantified 5mC at the lexA locus, and then examined the effect of LexA on Dcm activity, as well as the impact of this 5mC mark on LexA binding, lexA transcription, and SOS response induction. We found that 5mC at the lexA promoter is specific to stationary phase growth, but that it does not affect lexA expression. Our data support a model where LexA binding at the promoter inhibits Dcm activity without an effect on the SOS regulon.
细菌 DNA 损伤反应途径（SOS 反应）由一个受单一转录抑制剂 LexA 调控的基因网络组成。lexA 启动子本身包含两个 LexA 操作子，实现负反馈。在大肠杆菌中，下游操作子包含一个保守的 DNA 胞嘧啶甲基转移酶（Dcm）位点，该位点在静止期生长过程中被预测会特异性地甲基化为 5-甲基胞嘧啶（5mC），这表明 DNA 甲基化在 SOS 反应中具有调节作用。为了验证这一点，我们在 lexA 基因座上定量了 5mC，然后检测了 LexA 对 Dcm 活性的影响，以及这个 5mC 标记对 LexA 结合、lexA 转录和 SOS 反应诱导的影响。我们发现，lexA 启动子上的 5mC 是静止期生长特有的，但它不会影响 lexA 的表达。我们的数据支持这样一种模型，即 LexA 在启动子上的结合抑制了 Dcm 活性，而对 SOS 调控子没有影响。
