Fredrick K, Caramori T, Chen Y F, Galizzi A, Helmann J D
Section of Microbiology, Cornell University, Ithaca, NY 14853, USA.
Proc Natl Acad Sci U S A. 1995 Mar 28;92(7):2582-6. doi: 10.1073/pnas.92.7.2582.
Flagellin is one of the most abundant proteins in motile bacteria, yet its expression requires a low abundance sigma factor (sigma 28). We show that transcription from the Bacillus subtilis flagellin promoter is stimulated 20-fold by an upstream A+T-rich region [upstream promoter (UP) element] both in vivo and in vitro. This UP element is contacted by sigma 28 holoenzyme bound at the flagellin promoter and binds the isolated alpha 2 subassembly of RNA polymerase. The UP element increases the affinity of RNA polymerase for the flagellin promoter and stimulates transcription when initiation is limited by the rate of RNA polymerase binding. Comparison with other promoters in the flagellar regulon reveals a bipartite architecture: the -35 and -10 elements confer specificity for sigma 28, while promoter strength is determined largely by upstream DNA sequences.
鞭毛蛋白是运动细菌中含量最丰富的蛋白质之一，但其表达需要一种低丰度的σ因子（σ28）。我们发现，枯草芽孢杆菌鞭毛蛋白启动子的转录在体内和体外均受到上游富含A+T区域[上游启动子（UP）元件]的20倍刺激。该UP元件与结合在鞭毛蛋白启动子上的σ28全酶接触，并与RNA聚合酶的分离α2亚基结合。当起始受RNA聚合酶结合速率限制时，UP元件增加了RNA聚合酶对鞭毛蛋白启动子的亲和力并刺激转录。与鞭毛调节子中的其他启动子比较显示出一种二分结构：-35和-10元件赋予对σ28的特异性，而启动子强度很大程度上由上游DNA序列决定。
