The Third Pillar of Bacterial Signal Transduction: Signaling Diversity and Evolution of Extracytoplasmic Function (ECF) Sigma Factors

细菌对环境条件的适应需要跨膜信号转导来协调适当的细胞反应。启动子决定了转录起始的特异性和效率，因此是协调差异基因表达的重要调控开关。胞质外功能（Extracytoplasmic function， ECF） σ因子是最大和最多样化的一组可选σ因子，通过第二种通常是膜锚定的传感器蛋白，即相应的抗σ因子，对环境刺激作出反应。尽管它们数量丰富，总体上很重要，但迄今为止只有非常有限的数量得到了实验研究。在这里，我们提出了在综合比较基因组学和转录组学研究中发现的三个新的和不寻常的保守ECF σ因子组的成员进行分析，(i)参与地衣芽孢杆菌包膜应激反应的ECF σ因子。（ii） ECF σ因子在功能上与反应调节因子相关，但缺乏抗σ因子，表明信号转导的新机制。(3)参与氧化应激反应的ECF σ因子。这些蛋白在功能上与羧酸内酯脱羧酶同源物相连，而不是标准的抗σ因子。我们的分析（正在进行和建议）将嵌入到比较基因组学数据库中，并用于建立生物信息学工具，以重建和预测微生物基因组中ECF σ因子依赖的调控网络。

Adaptation of a bacterium to environmental conditions necessitates transmembrane signaltransduction to orchestrate adequate cellular responses. The promoter determines the specificity and efficiency of transcriptional initiation, and is therefore an important regulatory switchboard to coordinate differential gene expression. Extracytoplasmic function (ECF) σ factors, the largest and most diverse group of alternative σ factors, respond to environmental stimuli through a second, normally membraneanchored sensor protein, the corresponding anti-σ factor. Despite their abundance and overall importance, only a very limited number of these systems have been experimentally studied to date. Here we propose the analysis of members of three novel and unusual groups of conserved ECF σ factors that were identified during comprehensive comparative genomics and transcriptomics studies, (i) ECF σ factors involved in the cell envelope stress response of Bacillus licheniformis. (ii) ECF σ factors that are functionally linked to response regulators, but lack an anti-σ factor, indicative for a novel mechanism of signal transduction. (iii) ECF σ factors implicated to be involved in oxidative stress response. These proteins are functionally linked to carboxymuconolactone decarboxylase homologs instead of a standard anti-σ factor. Our analyses (ongoing and proposed) will be embedded in a comparative genomics database and used to establish bioinformatics tools to reconstruct and predict ECF σ factor-dependent regulatory networks in microbial genomes.