Abstract
The widespread CsrA/RsmA protein regulators repress translation by binding GGA motifs in bacterial mRNAs. CsrA activity is primarily controlled through sequestration by multiple small regulatory RNAs. Here we investigate CsrA activity control in the absence of antagonizing small RNAs by examining the CsrA regulon in the human pathogen Campylobacter jejuni. We use genome-wide co-immunoprecipitation combined with RNA sequencing to show that CsrA primarily binds flagellar mRNAs and identify the major flagellin mRNA (flaA) as the main CsrA target. The flaA mRNA is translationally repressed by CsrA, but it can also titrate CsrA activity. Together with the main C. jejuni CsrA antagonist, the FliW protein, flaA mRNA controls CsrA-mediated post-transcriptional regulation of other flagellar genes. RNA-FISH reveals that flaA mRNA is expressed and localized at the poles of elongating cells. Polar flaA mRNA localization is translation dependent and is post-transcriptionally regulated by the CsrA-FliW network. Overall, our results suggest a role for CsrA-FliW in spatiotemporal control of flagella assembly and localization of a dual-function mRNA.
Highlights
The widespread CsrA/RsmA protein regulators repress translation by binding GGA motifs in bacterial mRNAs
Our genome-wide approach reveals many mRNAs of flagellar genes as potential CsrA targets and we demonstrate that flagellin mRNA (flaA) mRNA, encoding the major flagellin, has dual function
Our study revealed the major flagellin mRNA is both the main CsrA target and a dualfunction mRNA, which can titrate CsrA activity together with the FliW protein, the main CsrA antagonist (Fig. 9)
Summary
The widespread CsrA/RsmA protein regulators repress translation by binding GGA motifs in bacterial mRNAs. Northern blot analysis showed flaA-3xFLAG mRNA levels are only mildly affected in the different mutant strains, further indicating post-transcriptional regulation of flaA by CsrA (Fig. 2b and Supplementary Fig. 8a).
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