Circuits mixtes de régulation entre petits ARN régulateurs et systèmes à deux composants chez Escherichia coli

Abstract : Small regulatory RNA (sRNAs) and two component systems (TCS) are both widespread regulators of gene expression in bacteria. While TCS are mostly transcriptional regulators, a large class of sRNAs acts as post-transcriptional regulators of gene expression by modulating translation and/or stability of target-mRNAs. Many connections have recently been unraveled between these two types of regulators, resulting in mixed regulatory circuits with poorly characterized properties.First, we have investigated in details the negative feedback circuit that exists between the EnvZ-OmpR TCS and the OmrA/B sRNAs in Escherichia coli. We have found that OmpR directly activates transcription from omrA and omrB promoters, allowing production of OmrA/B sRNAs that target multiple mRNAs through their conserved 5’ end, including the ompR-envZ mRNA. In agreement with previous reports, we have found that this control of ompR-envZ by OmrA/B sRNAs does not affect the amount of OmpR-P i.e. the presumably active form of the regulator. This phenomenon therefore raised the question of the possible interest of such a regulation. Thereafter, we found that OmrA/B regulation is really unique because they respond to the phosphorylated form but also to the unphosphorylated form of OmpR. As a result, OmrA/B limit their own synthesis while they have only a limited effect on others targets of OmpR, such as the OmpC or OmpF porins.This work led us to try to characterize other examples of modulation of two-component systems synthesis by small regulatory RNAs. In particular, we studied the regulation of the NarQ-NarP system. Indeed, our work showed that the synthesis of narP is controlled by the RprA sRNA. This regulation appears to affect NarP targets and in particular the napFDAGHBC operon. Moreover, RprA would respond to the same stimulus as the NarQ-NarP system, thus creating a physiological link between the small RNA and its target.Finally, another aspect of this work was to study the regulation of OmrA/B in a context of infection of macrophages by an Escherichia coli pathogenic strain, LF82. Indeed, data suggested that these small RNAs were induced during infection. I was able to validate these data and showed that this induction was dependent on the presence of the EnvZ-OmpR system.
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Anaïs Brosse. Circuits mixtes de régulation entre petits ARN régulateurs et systèmes à deux composants chez Escherichia coli. Microbiologie et Parasitologie. Université Sorbonne Paris Cité, 2017. Français. ⟨NNT : 2017USPCC245⟩. ⟨tel-02145666⟩

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