Etude de la conservation de la terminaison de la transcription Rho-dépendante au sein de la biodiversité

Abstract : The bacterial Rho factor is a ring-shaped, hexameric RNA helicase which uses the energy derived from ATP hydrolysis to translocate along RNA strands, disrupting molecular roadblocks in its way. A major function of Rho is to induce termination of transcription. Extensive studies of the prototypical Rho factor from E. coli (EcRho) indicate that the enzyme binds naked regions of nascent RNA transcripts at the level of Rut (Rho utilization) sites and, then, uses its ATPase-dependent translocase activity to catch up with RNA polymerase and to trigger dissociation of the transcription elongation complex. EcRho is implicated in 20 to 50 % of all transcription termination events in E. coli and contributes to the global regulation and protection of the bacterial genome through various sophisticated mechanisms. The limited spectrum of activity of the antibiotic Bicyclomycin (BCM) – an inhibitor of Rho’s ATPase – suggests that Rho, while critical in many Gram- species such as E. coli, is dispensable in most Gram+ species. To verify this assumption and better understand the importance of Rho across the biodiversity, we assessed the phylogenetic distribution and conservation of Rho using public ‘omics’ databases. We found Rho (or a rho ORF) in ~92% of analyzed species (representing most bacterial phyla), its presence seemingly related to the complexity of the bacterial genome, regulatory program, and ecosystem. An illustration of this complexity is our discovery that regulatory protein CsrA mediates Rho-dependent termination in the 5’UTR of the pgaABCD operon whose expression is critical for biofilm formation by E. coli. In parallel, we tested the recent proposal that the Rho factor of Mycobacterium tuberculosis (MtbRho) operates by an atypical, ATPase-independent mechanism that would make it immune to BCM. Our results rule out this possibility and unambiguously show that MtbRho uses a mechanism similar to that of EcRho, one that can be inhibited by BCM (albeit at unusually high concentrations). Overall, this work provides key, new information to better understand the role, mechanism, and importance of Rho across the bacterial diversity and endorses Rho as a promising target for the development of new antibiotics.
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François d' Heygere. Etude de la conservation de la terminaison de la transcription Rho-dépendante au sein de la biodiversité. Sciences agricoles. Université d'Orléans, 2015. Français. ⟨NNT : 2015ORLE2028⟩. ⟨tel-01320716⟩

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