Hickman Jason W, Harwood Caroline S
Department of Microbiology, University of Washington, Seattle, WA 98195, USA.
Mol Microbiol. 2008 Jul;69(2):376-89. doi: 10.1111/j.1365-2958.2008.06281.x.
High levels of the intracellular signalling molecule cyclic diguanylate (c-di-GMP) supress motility and activate exopolysaccharide (EPS) production in a variety of bacterial species. In many bacteria part of the effect of c-di-GMP is on gene expression, but the mechanism involved is not known for any species. We have identified the protein FleQ as a c-di-GMP-responsive transcriptional regulator in Pseudomonas aeruginosa. FleQ is known to activate expression of flagella biosynthesis genes. Here we show that it also represses transcription of genes including the pel operon involved in EPS biosynthesis, and that this repression is relieved by c-di-GMP. Our in vivo data indicate that FleQ represses pel transcription and that pel transcription is not repressed when intracellular c-di-GMP levels are high. FleN, a known antiactivator of FleQ also participates in control of pel expression. In in vitro experiments we found that FleQ binds to pel promoter DNA and that this binding is inhibited by c-di-GMP. FleQ binds radiolabelled c-di-GMP in vitro. FleQ does not have amino acid motifs that resemble previously defined c-di-GMP binding domains. Our results show that FleQ is a new type of c-di-GMP binding protein that controls the transcriptional regulation of EPS biosynthesis genes in P. aeruginosa.
在多种细菌中，细胞内信号分子环二鸟苷酸（c-di-GMP）水平升高会抑制运动性并激活胞外多糖（EPS）的产生。在许多细菌中，c-di-GMP的部分作用是影响基因表达，但对于任何物种而言，其涉及的机制尚不清楚。我们已确定蛋白FleQ是铜绿假单胞菌中一种对c-di-GMP有反应的转录调节因子。已知FleQ可激活鞭毛生物合成基因的表达。在此我们表明，它还会抑制包括参与EPS生物合成的pel操纵子在内的基因的转录，并且这种抑制作用可被c-di-GMP解除。我们的体内数据表明，FleQ会抑制pel转录，而当细胞内c-di-GMP水平较高时，pel转录不会受到抑制。FleN是一种已知的FleQ反激活因子，它也参与对pel表达的调控。在体外实验中，我们发现FleQ会与pel启动子DNA结合，并且这种结合会被c-di-GMP抑制。FleQ在体外会结合放射性标记的c-di-GMP。FleQ没有类似于先前定义的c-di-GMP结合结构域的氨基酸基序。我们的结果表明，FleQ是一种新型的c-di-GMP结合蛋白，可控制铜绿假单胞菌中EPS生物合成基因的转录调控。
