Laboratoire de Microbiologie-Signaux et Micro-Environnement, LMSM, Université de Rouen, Rouen, France.
J Bacteriol. 2012 Aug;194(16):4301-11. doi: 10.1128/JB.00509-12. Epub 2012 Jun 8.
The OprF porin is the major outer membrane protein of Pseudomonas aeruginosa. OprF is involved in several crucial functions, including cell structure, outer membrane permeability, environmental sensing, and virulence. The oprF gene is preceded by the sigX gene, which encodes the poorly studied extracytoplasmic function (ECF) sigma factor SigX. Three oprF promoters were previously identified. Two intertwined promoters dependent on σ(70) and SigX are located in the sigX-oprF intergenic region, whereas a promoter dependent on the ECF AlgU lies within the sigX gene. An additional promoter was found in the cmpX-sigX intergenic region. In this study, we dissected the contribution of each promoter region and of each sigma factor to oprF transcription using transcriptional fusions. In Luria-Bertani (LB) medium, the oprF-proximal region (sigX-oprF intergenic region) accounted for about 80% of the oprF transcription, whereas the AlgU-dependent promoter had marginal activity. Using the sigX mutant PAOSX, we observed that the SigX-dependent promoter was largely predominant over the σ(70)-dependent promoter. oprF transcription was increased in response to low NaCl or high sucrose concentrations, and this induced transcription was strongly impaired in the absence of SigX. The lack of OprF itself increased oprF transcription. Since these conditions led to cell wall alterations, oprF transcription could be activated by signals triggered by perturbation of the cell envelope.
OprF 孔蛋白是铜绿假单胞菌的主要外膜蛋白。OprF 参与了几个关键功能，包括细胞结构、外膜通透性、环境感应和毒力。oprF 基因之前是 sigX 基因，它编码了研究甚少的细胞外功能 (ECF) σ 因子 SigX。以前已经鉴定了三个 oprF 启动子。两个相互交织的依赖于 σ(70)和 SigX 的启动子位于 sigX-oprF 基因间区，而依赖于 ECF AlgU 的启动子位于 sigX 基因内。在 cmpX-sigX 基因间区还发现了一个额外的启动子。在这项研究中，我们使用转录融合来剖析每个启动子区域和每个 σ 因子对 oprF 转录的贡献。在 LB 培养基中，oprF 近端区域（sigX-oprF 基因间区）占 oprF 转录的约 80%，而 AlgU 依赖性启动子的活性则微不足道。使用 sigX 突变体 PAOSX，我们观察到 SigX 依赖性启动子在很大程度上优于 σ(70)依赖性启动子。oprF 转录在低盐或高蔗糖浓度下增加，而在没有 SigX 的情况下，这种诱导转录受到严重损害。OprF 的缺乏本身增加了 oprF 转录。由于这些条件导致细胞壁改变，因此 oprF 转录可能会被细胞包膜扰动引发的信号激活。
