Post-Transcriptional Regulation of RseA: Identification of Small RNAs That act as Novel Regulatory Switches During Envelope Stress

Bacteria may experience transient changes in their internal or external environments, affecting their ability to maintain homeostasis. One example is Envelope Stress. Envelope stress is the mis-folding or accumulation of outer membrane proteins (OMPs); resulting in aberrant growth and cellular replication. The adjusted global gene expression resulting from Envelope Stress is known as the as Envelope Stress Response (ESR). Initiation of the ESR in E. coli is through the alternative sigma factor, sigmaE (RpoE). RpoE initiates the transcription of several periplasmic proteases and small regulatory RNAs (sRNAs) that down-regulate OMP expression alleviating envelope stress. RpoE is regulated at the level of activity through its anti-sigma factor, RseA.;RseA is an anti-sigma factor that plays a central role in the envelope stress response in E. coli. The rseA gene is in an operon with its target, rpoE, upstream of it. Recently, a sigmaE dependent promoter of the rseA gene was mapped within the rpoE gene, yielding a 228 nucleotide long 5' untranslated region (UTR). In E. coli, the presence of a long 5' UTR is one clue into possible post-transcriptional regulation by sRNAs. However, there are no reports of post-transcriptional regulation of the RseAP3 transcript by sRNAs.;We identified two small RNA regulators of RseA, the iron regulated sRNA RyhB and the anaerobiosis-regulated sRNA FnrS, through a targeted genetic screen. Through genetic analysis, our results suggest that RyhB, and possibly FnrS, act through direct base-pairing with the RseA mRNA to regulate RseA. This research also supports a possible link between iron-regulation and envelope stress in E. coli..