sRNA roles in regulating transcriptional regulators: Lrp and SoxS regulation by sRNAs

Post-transcriptional regulation of transcription factors contributes to regulatory circuits. We created translational reporter fusions for multiple central regulators in Escherichia coli and examined the effect of Hfq-dependent non-coding RNAs on these fusions. This approach yields an ‘RNA landscape,’ identifying Hfq-dependent sRNAs that regulate a given fusion. No significant sRNA regulation of crp or fnr was detected. hns was regulated only by DsrA, as previously reported. Lrp and SoxS were both found to be regulated post-transcriptionally. Lrp, ‘leucine-responsive regulatory protein,’ regulates genes involved in amino acid biosynthesis and catabolism and other cellular functions. sRNAs DsrA, MicF and GcvB each independently downregulate the lrp translational fusion, confirming previous reports for MicF and GcvB. MicF and DsrA interact with an overlapping site early in the lrp ORF, while GcvB acts upstream at two independent sites in the long lrp leader. Surprisingly, GcvB was found to be responsible for significant downregulation of lrp after oxidative stress; MicF also contributed. SoxS, an activator of genes used to combat oxidative stress, is negatively regulated by sRNA MgrR. This study demonstrates that while not all global regulators are subject to sRNA regulation, post-transcriptional control by sRNAs allows multiple environmental signals to affect synthesis of the transcriptional regulator.