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Accueil > Départements > Biologie des Génomes > Maria COSTA : Structure, Fonction et Evolution des Retrotransposons Bactériens

Publications de l’équipe


  • M. Costa, H. Walbott, D. Monachello, E. Westhof, et F. Michel, « Crystal structures of a group II intron lariat primed for reverse splicing », Science (New York, N.Y.), vol. 354, nᵒ 6316, 2016.
    Résumé : The 2'-5' branch of nuclear premessenger introns is believed to have been inherited from self-splicing group II introns, which are retrotransposons of bacterial origin. Our crystal structures at 3.4 and 3.5 angstrom of an excised group II intron in branched ("lariat") form show that the 2'-5' branch organizes a network of active-site tertiary interactions that position the intron terminal 3'-hydroxyl group into a configuration poised to initiate reverse splicing, the first step in retrotransposition. Moreover, the branchpoint and flanking helices must undergo a base-pairing switch after branch formation. A group II-based model of the active site of the nuclear splicing machinery (the spliceosome) is proposed. The crucial role of the lariat conformation in active-site assembly and catalysis explains its prevalence in modern splicing.
    Mots-clés : DBG, RIBOZYMO, RNASTR.

  • D. Monachello, F. Michel, et M. Costa, « Activating the branch-forming splicing pathway by reengineering the ribozyme component of a natural group II intron », RNA (New York, N.Y.), vol. 22, nᵒ 3, p. 443-455, 2016.
    Résumé : When assayed in vitro, group IIC self-splicing introns, which target bacterial Rho-independent transcription terminators, generally fail to yield branched products during splicing despite their possessing a seemingly normal branchpoint. Starting with intron O.i.I1 from Oceanobacillus iheyensis, whose crystallographically determined structure lacks branchpoint-containing domain VI, we attempted to determine what makes this intron unfit for in vitro branch formation. A major factor was found to be the length of the helix at the base of domain VI: 4 base pairs (bp) are required for efficient branching, even though a majority of group IIC introns have a 3-bp helix. Equally important for lariat formation is the removal of interactions between ribozyme domains II and VI, which are specific to the second step of splicing. Conversely, mismatching of domain VI and its proposed first-step receptor in subdomain IC1 was found to be detrimental; these data suggest that the intron-encoded protein may promote branch formation partly by modulating the equilibrium between conformations specific to the first and second steps of splicing. As a practical application, we show that by making just two changes to the O.i.I1 ribozyme, it is possible to generate sufficient amounts of lariat intron for the latter to be purified and used in kinetic assays in which folding and reaction are uncoupled.
    Mots-clés : Bacillus, DBG, group II intron, Introns, lariat intron, linear intron, Phylogeny, RIBOZYMO, RNA Splicing, RNA, Catalytic, self-splicing.
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Publications Principales avant 2015

- Costa M*, Monachello D (2014) Probing RNA folding by hydroxyl radical footprinting.
Methods Mol Biol. 1086:119-42.

- Li CF, Costa M, Michel F (2011) Linking the branchpoint helix to a newly found receptor allows lariat formation by a group II intron. EMBO J . 30(15):3040-51.

- Li CF, Costa M, Bassi G, Lai YK, Michel F (2011) Recurrent insertion of 5’-terminal nucleotides and loss of the branchpoint motif in lineages of group II introns inserted in mitochondrial preribosomal RNAs. RNA . 17:1321-35.

- Mullineux ST, Costa M, Bassi GS, Michel F, Hausner G (2010) A group II intron encodes a functional LAGLIDADG homing endonuclease and self-splices under moderate temperature and ionic conditions. RNA . 16:1818-31.

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