High abundance of leaderless mRNAs and a novel stress response mechanism in radiation resistant Deinococcus bacteria

Orateur : Laurence BLANCHARD ((Laboratoire de Bioénergétique Cellulaire - Institut de Biosciences et Biotechnologies d’Aix-Marseille (BIAM) - CEA Cadarache)

Deinococcus bacteria are famous for their extreme tolerance to gamma and UV radiation, to desiccation and to other DNA damage and oxidative stress-generating conditions, which is related to their capacity to repair massive DNA damage. Radiation tolerance might result from a combination of different molecular mechanisms and physiological determinants. However, this extreme resistance has not yet been fully explained. We are studying the Sahara bacterium Deinococcus deserti. We analysed its genome using a proteogenomic approach and its transcriptome using differential RNA sequencing. Strikingly, this revealed an exceptionally high proportion (60%) of leaderless mRNAs (i.e. lacking a 5’-untranslated region). The importance in radio-tolerance of this translation initiation mechanism will be discussed. In the Deinococcus, the upregulated expression of various genes after stress (including recA) requires the constitutively expressed protein IrrE. We solved its crystal structure and recently demonstrated that IrrE is a metalloprotease that cleaves and inactivates a transcriptional repressor, DdrO, after irradiation. This constitutes a novel stress response mechanism. Interestingly, protein pairs similar to IrrE/DdrO have also been identified as potential new toxin/anti-toxin systems in bacteria, including pathogens such as Streptococcus pneumoniae.

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