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2 octobre 2018: 2 événements

  • Evènements I2BC

    Mardi 2 octobre 11:00-12:00 - Thierry Touzé - Département Microbiologie, I2BC

    Insights into biogenesis of bacterial cell-wall and recycling of bactoprenol, the peptidoglycan subunit carrier lipid

    Lieu : Auditorium I2BC - Bât. 21, Campis Gif

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  • Evènements I2BC

    Mardi 2 octobre 14:00-15:30 - Jinwei Zhang - National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, USA

    Feast or famine - amino acid sensing on the tRNA by a mRNA

    Résumé : Amino acids are among the most ubiquitous and essential nutrients. T-box riboswitches are bacterial cis-regulatory noncoding RNAs that regulate amino acid-metabolic genes through multipartite interactions with tRNAs [1]. T-boxes share a phylogenetically conserved architecture comprised of two domains — a 5’ Stem I and 3’ antiterminator domain and a linker. Stem I selectively docks a cognate tRNA via sequence- and structure-specific interactions [2-4]. The antiterminator probes the molecular volume of the docked tRNA 3’ end to sense aminoacylation [5]. This readout dictates the formation of either an intrinsic transcription terminator or antiterminator. The architecture of a full-length T-box complex and detailed interactions between the tRNA 3’ region and the antiterminator remain poorly understood.
    We define a minimal region of the T-box both necessary and sufficient to selectively bind an uncharged tRNA, and report a 2.7 Å co-crystal structure of the complex. The structure reveals how tRNA 3’ end is buried inside the antiterminator such that a conserved G•U wobble pair at the base of helix A2 abuts the ribose 3’-OH of the tRNA terminal adenosine. This juxtaposition creates steric clash between the universal amino group of the esterified amino acid and the uridine nucleobase, thus providing a general mechanism to reject any aminoacyl-tRNA. Interestingly, the clash is exasperated by the outward shift of the wobble uridine into the major groove. We compare this RNA-based steric device to ribosome-bound RelA, which positions a beta strand to reject aminoacyl-tRNA in stringent response [6-7].
    Further, we report a cryo-EM structure of a full-length T-box riboswitch-tRNA complex, which reveals a surprisingly ordered inter- domain linker. Together, the structures show that extensive intermolecular stacking allows Stem I and antiterminator domains of the T-box to sandwich the uncharged tRNA to form a 30-bp continuous stack, to stabilize the antiterminator to transcribe downstream genes.
    1. Grundy & Henkin, Cell 1993 ; 2. Grigg & Ke, Structure 2013 ; 3. Zhang & Ferré-D’Amaré, Nature 2013 ; 4. Zhang & Ferré-D’Amaré, Structure 2014 ; 5. Zhang & Ferré-D’Amaré, Mol Cell 2014 ; 6. Brown et al., Nature 2016 ; 7. Loveland et al., eLife 2016. Supported in part by the intramural research program of NIDDK, NIH.

    Lieu : Auditorium I2BC - Bât. 21, Campus Gif

    En savoir plus : Evènements I2BC