Department of Microbiology, Cornell University, Ithaca, NY 14853-8101, USA.
Nucleic Acids Res. 2018 Jan 9;46(1):134-145. doi: 10.1093/nar/gkx953.
The ability of bacteria to adapt to stress depends on the conditional expression of specific sets of genes. Bacillus subtilis encodes seven extracytoplasmic function (ECF) sigma (σ) factors that regulate functions important for survival under conditions eliciting cell envelope stress. Of these, four have been studied in detail: σM, σW, σX and σV. These four σ factors recognize overlapping sets of promoters, although the sequences that determine this overlapping recognition are incompletely understood. A major role in promoter selectivity has been ascribed to the core -10 and -35 promoter elements. Here, we demonstrate that a homopolymeric T-tract motif, proximal to the -35 element, functions in combination with the core promoter sequences to determine selectivity for ECF sigma factors. This motif is most critical for promoter activation by σV, and contributes variably to activation by σM, σX and σW. We propose that this motif, which is a feature of the deduced promoter consensus for a subset of ECF σ factors from many species, imparts intrinsic DNA curvature to influence promoter activity. The differential effect of this region among ECF σ factors thereby provides a mechanism to modulate the nature and extent of regulon overlap.
细菌适应压力的能力取决于特定基因集的条件表达。枯草芽孢杆菌编码七种细胞外功能（ECF）σ（σ）因子，这些因子调节在引发细胞包膜应激的条件下生存的重要功能。其中，有四个已经被详细研究：σM、σW、σX 和 σV。这四个 σ 因子识别重叠的启动子集，尽管决定这种重叠识别的序列尚未完全理解。核心-10 和-35 启动子元件被认为在启动子选择性中起主要作用。在这里，我们证明了靠近-35 元件的同聚 T 链段基序与核心启动子序列一起起作用，以确定 ECF σ 因子的选择性。该基序对于 σV 的启动子激活最为关键，并在不同程度上有助于 σM、σX 和 σW 的激活。我们提出，该基序是许多物种中一组 ECF σ 因子推断的启动子共识的特征，赋予了固有 DNA 曲率以影响启动子活性。因此，ECF σ 因子之间该区域的差异效应提供了一种调节调控基因重叠性质和程度的机制。
