RpoS-dependent transcriptional control of sprE: Regulatory feedback loop

The stationary-phase response exhibited by Escherichia coli upon nutrient s tarvation is mainly induced by a decrease of the ClpXP-dependent degradatio n of the alternate primary or factor RpoS. Although it is known that the sp ecific regulation of this proteolysis is exercised by the orphan response r egulator SprE, it remains unclear how SprE's activity is regulated in vivo. Previous studies have demonstrated that the cellular content of SprE itsel f 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 i s part of the two-gene rssA-sprE operon, but it can also be transcribed fro m 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 R ssA does not regulate either SprE or RpoS under the conditions tested.