Ruiz N, Peterson C N, Silhavy T J
Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA.
J Bacteriol. 2001 Oct;183(20):5974-81. doi: 10.1128/JB.183.20.5974-5981.2001.
The stationary-phase response exhibited by Escherichia coli upon nutrient starvation is mainly induced by a decrease of the ClpXP-dependent degradation of the alternate primary sigma factor RpoS. Although it is known that the specific regulation of this proteolysis is exercised by the orphan response regulator SprE, it remains unclear how SprE's activity is regulated in vivo. Previous studies have demonstrated that the cellular content of SprE itself is paradoxically increased in stationary-phase cells in an RpoS-dependent fashion. We show here that this RpoS-dependent upregulation of SprE levels is due to increased transcription. Furthermore, we demonstrate that sprE is part of the two-gene rssA-sprE operon, but it can also be transcribed from an additional RpoS-dependent promoter located in the rssA-sprE intergenic region. In addition, by using an in-frame deletion in rssA we found that RssA does not regulate either SprE or RpoS under the conditions tested.
大肠杆菌在营养饥饿时表现出的稳定期反应主要是由替代主要σ因子RpoS的ClpXP依赖性降解减少所诱导的。尽管已知这种蛋白水解的特异性调节是由孤儿反应调节因子SprE行使的，但尚不清楚SprE的活性在体内是如何调节的。先前的研究表明，SprE自身的细胞含量在稳定期细胞中以RpoS依赖性方式反常增加。我们在此表明，SprE水平的这种RpoS依赖性上调是由于转录增加所致。此外，我们证明sprE是双基因rssA-sprE操纵子的一部分，但它也可以从位于rssA-sprE基因间区域的另一个RpoS依赖性启动子转录。另外，通过在rssA中使用框内缺失，我们发现在测试条件下RssA不调节SprE或RpoS。
