The rpoN operon, an important regulatory hub in Enterobacteriaceae, includes rpoN encoding sigma factor σ⁵⁴, hpf involved in ribosome hibernation, rapZ regulating glucosamine-6-phosphate levels, and two genes encoding proteins of the nitrogen-related phosphotransferase system. Little is known about regulatory mechanisms controlling the abundance of these proteins. This study employs transposon mutagenesis and chemical screens to dissect the complex expression of the rpoN operon. We find that envelope stress conditions trigger read-through transcription into the rpoN operon from a promoter located upstream of the preceding lptA-lptB locus. This promoter is controlled by the envelope stress sigma factor E and response regulator PhoP is required for its full response to a subset of stress signals. σ^E also stimulates ptsN-rapZ-npr expression using an element downstream of rpoN, presumably by interfering with mRNA processing by RNase E. Additionally, we identify a novel promoter in the 3′ end of rpoN that directs transcription of the distal genes in response to ethanol. Finally, we show that translation of hpf and ptsN is individually regulated by the RNA chaperone Hfq, perhaps involving small RNAs. Collectively, our work demonstrates that the rpoN operon is subject to complex regulation, integrating signals related to envelope stress and carbon source quality.

中文翻译：

---

包括细胞包膜应激在内的多种调控输入协调大肠杆菌 rpoN 操纵子的表达


rpoN操纵子是肠杆菌科的重要调节中心，包括编码σ因子^σ54的rpoN 、参与核糖体冬眠的hpf 、调节6-磷酸葡萄糖胺水平的rapZ以及编码氮相关磷酸转移酶系统蛋白的两个基因。人们对控制这些蛋白质丰度的调控机制知之甚少。本研究采用转座子诱变和化学筛选来剖析rpoN操纵子的复杂表达。我们发现包膜应激条件触发从位于前面的lptA - lptB基因座上游的启动子到rpoN操纵子的通读转录。该启动子由包络应激西格玛因子 E 控制，并且需要响应调节因子 PhoP 来完全响应应激信号的子集。 σ ^E还使用rpoN下游的元件刺激ptsN-rapZ-npr表达，推测是通过干扰 RNase E 的 mRNA 加工。此外，我们在rpoN的 3' 端发现了一个新的启动子，它指导远端基因的转录以响应至乙醇。最后，我们证明hpf和ptsN的翻译分别受到 RNA 伴侣 Hfq 的调节，可能涉及小 RNA。总的来说，我们的工作表明rpoN操纵子受到复杂的调控，整合与包膜应力和碳源质量相关的信号。