Wray L V, Ferson A E, Fisher S H
Department of Microbiology, Boston University School of Medicine, Massachusetts 02118, USA.
J Bacteriol. 1997 Sep;179(17):5494-501. doi: 10.1128/jb.179.17.5494-5501.1997.
Expression of urease, which is encoded by the ureABC operon, is regulated in response to nitrogen availability in Bacillus subtilis. Three ureABC promoters were identified in primer extension experiments and by examination of beta-galactosidase expression from ure-lacZ fusions. P1, a low-level constitutive promoter, lies immediately upstream of ureA. The P2 promoter is transcribed by the E sigmaH form of RNA polymerase and initiates transcription 270 bp upstream of the ureA start codon. The transcriptional start site for the sigmaA-dependent P3 promoter is located 839 bp upstream of the ureA start codon. To identify transcription factors that control ureABC expression, regulation of the P2 and P3 promoters was examined in wild-type and mutant strains. During rapid growth in minimal medium containing glucose and amino acids, CodY represses expression of the P2 and P3 promoters 30- and 60-fold, respectively. TnrA activates expression of the P3 promoter 10-fold in nitrogen-limited cells, while GlnR represses transcription from the P3 promoter 55-fold during growth on excess nitrogen. Expression of the ureABC operon increases 10-fold at the end of exponential growth in nutrient sporulation medium. This elevation in expression results from the relief of CodY-mediated repression during exponential growth and increased sigmaH-dependent transcription during stationary phase.
脲酶由脲ABC操纵子编码，其表达在枯草芽孢杆菌中受氮可用性的调节。在引物延伸实验以及通过检测脲 - lacZ融合体的β - 半乳糖苷酶表达中，鉴定出了三个脲ABC启动子。P1是一个低水平组成型启动子，位于ureA的紧邻上游。P2启动子由RNA聚合酶的E σH形式转录，在ureA起始密码子上游270 bp处起始转录。依赖σA的P3启动子的转录起始位点位于ureA起始密码子上游839 bp处。为了鉴定控制脲ABC表达的转录因子，在野生型和突变菌株中检测了P2和P3启动子的调控情况。在含有葡萄糖和氨基酸的基本培养基中快速生长期间，CodY分别将P2和P3启动子的表达抑制30倍和60倍。在氮限制细胞中，TnrA将P3启动子的表达激活10倍，而在过量氮条件下生长时，GlnR将P3启动子的转录抑制55倍。在营养芽孢形成培养基中指数生长末期，脲ABC操纵子的表达增加10倍。这种表达升高是由于指数生长期间CodY介导的抑制作用解除以及稳定期σH依赖性转录增加所致。
