Andersen J T, Jensen K F, Poulsen P
Enzyme Division, University of Copenhagen, Denmark.
Mol Microbiol. 1991 Feb;5(2):327-33. doi: 10.1111/j.1365-2958.1991.tb02113.x.
Expression of the Escherichia coli pyrE gene is regulated by transcription attenuation in the intercistronic orfE-pyrE region and modulated by the distance between the transcribing RNA polymerase and the leading ribosome as a function of the supply of UTP and GTP. In this communication we show that pyrE expression is hyper-repressed in vivo following addition of uracil in strains carrying the nusAcs10 mutation. This phenotype, previously seen in rpsL1204 strains whose ribosomes are pseudodependent on streptomycin and work at suboptimal elongation rate, indicates that RNA polymerase escapes from the ribosomes in the pyrE attenuator region in the nusA mutant. In vitro transcription studies revealed that the build-up of the full-length attenuated orfE transcript occurred more slowly in the presence of the NusA protein than in its absence. Moreover, the NusA protein enhanced several transcription pauses through the orfE gene. These effects were more pronounced when low concentrations of either UTP or GTP were used than at low concentrations of either CTP or ATP. The results indicate that the NusA protein is required for proper regulation of pyrE gene expression and is involved, together with the NTP pools, in maintaining the coupling between transcription and translation in the pyrE attenuator region by inhibiting RNA chain elongation.
大肠杆菌pyrE基因的表达受基因间orfE - pyrE区域转录衰减的调控，并受转录RNA聚合酶与领先核糖体之间距离的调节，该距离是UTP和GTP供应的函数。在本通讯中，我们表明，在携带nusAcs10突变的菌株中添加尿嘧啶后，pyrE表达在体内被超抑制。这种表型先前在rpsL1204菌株中观察到，其核糖体假依赖于链霉素且以次优延伸速率工作，这表明在nusA突变体中，RNA聚合酶在pyrE衰减子区域从核糖体上逃脱。体外转录研究表明，在存在NusA蛋白的情况下，全长衰减orfE转录本的积累比不存在时更慢。此外，NusA蛋白增强了通过orfE基因的几个转录暂停。当使用低浓度的UTP或GTP时，这些效应比使用低浓度的CTP或ATP时更明显。结果表明，NusA蛋白是正确调节pyrE基因表达所必需的，并且与NTP库一起，通过抑制RNA链延伸参与维持pyrE衰减子区域转录与翻译之间的偶联。
