Qi F X, Doi R H
Department of Biochemistry and Biophysics, University of California, Davis 95616.
J Bacteriol. 1990 Oct;172(10):5631-6. doi: 10.1128/jb.172.10.5631-5636.1990.
The presence of a second SigH promoter in the sigA operon of Bacillus subtilis was demonstrated by use of a promoter probe plasmid, a sigH deletion mutant, primer extension studies, and in vitro transcription with E sigma H holoenzyme. Both SigH promoters were expressed at low levels even during the growth phase but were expressed at higher levels during the early stationary phase. Expression from the upstream SigH promoter allowed the expression of both dnaE and sigA genes; however, expression from the downstream SigH promoter, which was located in the ribosome-binding site of the dnaE gene, resulted only in the expression of the sigA gene, since the truncated dnaE ribosome-binding site could not be used for initiating translation. Thus, promoter switching during the early stationary phase resulted not only in expression from SigH promoters but also in differential expression of the genes in the sigA operon.
通过使用启动子探针质粒、sigH缺失突变体、引物延伸研究以及用E sigma H全酶进行体外转录，证实了枯草芽孢杆菌sigA操纵子中存在第二个SigH启动子。即使在生长阶段，两个SigH启动子的表达水平都很低，但在稳定期早期表达水平较高。上游SigH启动子的表达使得dnaE和sigA基因都得以表达；然而，位于dnaE基因核糖体结合位点的下游SigH启动子的表达仅导致sigA基因的表达，因为截短的dnaE核糖体结合位点不能用于起始翻译。因此，在稳定期早期的启动子切换不仅导致了SigH启动子的表达，还导致了sigA操纵子中基因的差异表达。
