Laboratory of Molecular Biology, National Cancer Institute, Bethesda, MD 20892, USA.
Mol Microbiol. 2013 Jul;89(1):52-64. doi: 10.1111/mmi.12257. Epub 2013 May 31.
The PhoQ/PhoP two-component system activates many genes for lipopolysaccharide (LPS) modification when cells are grown at low Mg(2+) concentrations. An additional target of PhoQ and PhoP is MgrR, an Hfq-dependent small RNA that negatively regulates expression of eptB, also encoding a protein that carries out LPS modification. Examination of LPS confirmed that MgrR effectively silences EptB; the phosphoethanolamine modification associated with EptB is found in ΔmgrR::kan but not mgrR(+) cells. Sigma E has been reported to positively regulate eptB, although the eptB promoter does not have the expected Sigma E recognition motifs. The effects of Sigma E and deletion of mgrR on levels of eptB mRNA were independent, and the same 5' end was found in both cases. In vitro transcription and the behaviour of transcriptional and translational fusions demonstrate that Sigma E acts directly at the level of transcription initiation for eptB, from the same start point as Sigma 70. The results suggest that when Sigma E is active, synthesis of eptB transcript outstrips MgrR-dependent degradation; presumably the modification of LPS is important under these conditions. Adding to the complexity of eptB regulation is a second sRNA, ArcZ, which also directly and negatively regulates eptB.
当细胞在低镁（Mg2+）浓度下生长时，PhoQ/PhoP 双组分系统会激活许多用于脂多糖（LPS）修饰的基因。PhoQ 和 PhoP 的另一个靶标是 MgrR，这是一种依赖于 Hfq 的小 RNA，它负调控编码进行 LPS 修饰的蛋白的 eptB 的表达。对 LPS 的检查证实了 MgrR 能有效地沉默 EptB；与 EptB 相关的磷酸乙醇胺修饰在ΔmgrR::kan 中而不是 mgrR(+)细胞中发现。Sigma E 已被报道能正向调节 eptB，尽管 eptB 启动子没有预期的 Sigma E 识别基序。Sigma E 的作用和 mgrR 的缺失对 eptB mRNA 水平的影响是独立的，在这两种情况下都发现了相同的 5' 端。体外转录和转录及翻译融合物的行为表明，Sigma E 直接在 eptB 的转录起始水平起作用，与 Sigma 70 的起始点相同。结果表明，当 Sigma E 活跃时，eptB 转录本的合成超过了 MgrR 依赖的降解；推测在这些条件下，LPS 的修饰很重要。eptB 调节的复杂性增加了第二个 sRNA，ArcZ，它也直接负调控 eptB。
