Typas Athanasios, Hengge Regine
Institut für Biologie-Mikrobiologie, Freie Universität Berlin, Königin-Luise-Str 12-16, 14195 Berlin, Germany.
Mol Microbiol. 2005 Jan;55(1):250-60. doi: 10.1111/j.1365-2958.2004.04382.x.
The sigma(s) subunit of RNA polymerase (RNAP) is the master regulator of the general stress response in Escherichia coli. Nevertheless, the selectivity of promoter recognition by the housekeeping sigma70-containing and sigma5-containing RNAP holoenzymes (Esigma70 and Esigma(s) respectively) is not yet fully clarified, as they both recognize nearly identical -35 and -10 promoter consensus sequences. In this study, we show that in a subset of promoters, Esigma(s) favours the presence of a distal UP-element half-site, and at the same time is unable to take advantage of a proximal half-site or a full UP-element. This is reflected by the frequent occurrence of distal UP-element half-sites in natural sigma(s)-dependent promoters and the absence of proximal half-sites. Esigma70, however, exhibits the opposite preference. The presence of the -35 element is a prerequisite for this differential behaviour. In the absence of the -35 element, half or full UP-element sites play no role in sigma selectivity, but the distal subsite leads to an equivalent, if not greater, transcriptional stimulation than the proximal one for both sigma factors. Finally, experiments using single amino acid substitutions of sigma(s) indicate that the foundation for this preference lies in an inability of sigma(s) to interact with the a subunit C-terminal domain.
RNA聚合酶（RNAP）的σ亚基是大肠杆菌一般应激反应的主要调节因子。然而，含管家σ70的RNAP全酶（分别为Esigma70）和含σ5的RNAP全酶（Esigma(s)）对启动子识别的选择性尚未完全阐明，因为它们都识别几乎相同的 -35和 -10启动子共有序列。在本研究中，我们表明，在一部分启动子中，Esigma(s)倾向于存在远端UP元件半位点，同时无法利用近端半位点或完整的UP元件。这体现在天然σ(s)依赖型启动子中远端UP元件半位点的频繁出现以及近端半位点的缺失。然而，Esigma70表现出相反的偏好。-35元件的存在是这种差异行为的先决条件。在没有 -35元件的情况下，半或完整的UP元件位点在σ选择性中不起作用，但对于两种σ因子，远端亚位点导致的转录刺激与近端亚位点相当，甚至更大。最后，使用σ(s)的单氨基酸取代进行的实验表明，这种偏好的基础在于σ(s)无法与α亚基C末端结构域相互作用。
