Lee Eun-Hee, Hill Stuart A, Napier Ruth, Shafer William M
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA.
Mol Microbiol. 2006 Jun;60(6):1381-400. doi: 10.1111/j.1365-2958.2006.05185.x.
The farAB operon encodes an efflux pump system that mediates the resistance of Neisseria gonorrhoeae to antimicrobial long-chain fatty acids. We previously observed that expression of farAB is negatively regulated by the FarR repressor. In this study, we examined the molecular mechanism by which FarR represses expression of farAB. DNase I footprinting analysis, coupled with a deletion analysis of the farAB promoter region, indicated that FarR binds to three sites (termed sites A, B and C) within the DNA sequence upstream of farA; genetic analysis revealed, however, that site B is not required for FarR repression of farAB. This repression also required the presence of Integration Host Factor (IHF), which was found to bind to sequences located between FarR binding sites A and C. We determined that IHF binding to the farAB promoter region could inhibit transcription in vitro and that such binding induced a bending of the target DNA, which we propose to be important in regulating this operon. IHF binding to the promoter region was found to stabilize the binding of FarR to its binding sites A and C and as a consequence, enhanced repression of farAB expression mediated by FarR. We propose a model in which expression of the farAB-encoded efflux pump in N. gonorrhoeae is modulated by the DNA binding activities of FarR and IHF.
farAB操纵子编码一种外排泵系统，该系统介导淋病奈瑟菌对抗菌长链脂肪酸的抗性。我们之前观察到farAB的表达受FarR阻遏物的负调控。在本研究中，我们研究了FarR抑制farAB表达的分子机制。DNA酶I足迹分析以及farAB启动子区域的缺失分析表明，FarR结合在farA上游DNA序列中的三个位点（称为位点A、B和C）；然而，遗传分析显示，位点B对于FarR抑制farAB并非必需。这种抑制还需要整合宿主因子（IHF）的存在，发现IHF结合在FarR结合位点A和C之间的序列上。我们确定IHF与farAB启动子区域的结合可在体外抑制转录，并且这种结合诱导了靶DNA的弯曲，我们认为这对调控该操纵子很重要。发现IHF与启动子区域的结合可稳定FarR与其结合位点A和C的结合，因此增强了FarR介导的farAB表达的抑制。我们提出了一个模型，其中淋病奈瑟菌中farAB编码的外排泵的表达受FarR和IHF的DNA结合活性调控。
