Shen Aimee, Higgins Darren E
Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS Pathog. 2006 Apr;2(4):e30. doi: 10.1371/journal.ppat.0020030. Epub 2006 Apr 14.
Flagella are surface structures critical for motility and virulence of many bacterial species. In Listeria monocytogenes, MogR tightly represses expression of flagellin (FlaA) during extracellular growth at 37 degrees C and during intracellular infection. MogR is also required for full virulence in a murine model of infection. Using in vitro and in vivo infection models, we determined that the severe virulence defect of MogR-negative bacteria is due to overexpression of FlaA. Specifically, overproduction of FlaA in MogR-negative bacteria caused pleiotropic defects in bacterial division (chaining phenotype), intracellular spread, and virulence in mice. DNA binding and microarray analyses revealed that MogR represses transcription of all known flagellar motility genes by binding directly to a minimum of two TTTT-N5-AAAA recognition sites positioned within promoter regions such that RNA polymerase binding is occluded. Analysis of MogR protein levels demonstrated that modulation of MogR repression activity confers the temperature-specificity to flagellar motility gene expression. Epistasis analysis revealed that MogR repression of transcription is antagonized in a temperature-dependent manner by the DegU response regulator and that DegU further regulates FlaA levels through a posttranscriptional mechanism. These studies provide the first known example to our knowledge of a transcriptional repressor functioning as a master regulator controlling nonhierarchal expression of flagellar motility genes.
鞭毛是许多细菌物种运动性和毒力的关键表面结构。在单核细胞增生李斯特菌中，MogR在37℃的细胞外生长期间以及细胞内感染期间严格抑制鞭毛蛋白（FlaA）的表达。在小鼠感染模型中，MogR对于完全毒力也是必需的。利用体外和体内感染模型，我们确定MogR阴性细菌的严重毒力缺陷是由于FlaA的过表达。具体而言，MogR阴性细菌中FlaA的过量产生导致细菌分裂（成链表型）、细胞内传播和小鼠毒力方面的多效性缺陷。DNA结合和微阵列分析表明，MogR通过直接结合位于启动子区域内的至少两个TTTT-N5-AAAA识别位点来抑制所有已知鞭毛运动基因的转录，从而阻止RNA聚合酶结合。对MogR蛋白水平的分析表明，MogR抑制活性的调节赋予了鞭毛运动基因表达的温度特异性。上位性分析表明，MogR的转录抑制作用在温度依赖性方式下被DegU反应调节因子拮抗，并且DegU通过转录后机制进一步调节FlaA水平。据我们所知，这些研究提供了第一个已知的转录抑制因子作为控制鞭毛运动基因非层次表达的主调节因子发挥作用的例子。
