title: Speciation of a group I intron into a lariat capping ribozyme.
abstract: The lariat-capping (LC) ribozyme is a natural ribozyme isolated from eukaryotic microorganisms. Despite apparent structural similarity to group I introns, the LC ribozyme catalyzes cleavage by a 2',5' branching reaction, leaving the 3' product with a 3-nt lariat cap that functionally substitutes for a conventional mRNA cap in the downstream pre-mRNA encoding a homing endonuclease. We describe the crystal structures of the precleavage and postcleavage LC ribozymes, which suggest that structural features inherited from group I ribozymes have undergone speciation due to profound changes in molecular selection pressure, ultimately giving rise to an original branching ribozyme family. The structures elucidate the role of key elements that regulate the activity of the LC ribozyme by conformational switching and suggest a mechanism by which the signal for branching is transmitted to the catalytic core. The structures also show how conserved interactions twist residues, forming the lariat to join chemical groups involved in branching.
authors.affiliation: Architecture et Réactivité de l'ARN, Unité Propre de Recherche 9002, Institut de Biologie Moléculaire et Cellulaire, Université de Strasbourg, Centre National de la Recherche Scientifique, 67084 Strasbourg, France;
authors.forename: Mélanie
authors.initials: M
authors.lastname: Meyer
authors.affiliation: Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark;
authors.forename: Henrik
authors.initials: H
authors.lastname: Nielsen
authors.affiliation: Swiss Light Source at Paul Scherrer Institute, 5232 Villigen, Switzerland;
authors.forename: Vincent
authors.initials: V
authors.lastname: Oliéric
authors.affiliation: Synchrotron Soleil, 91190 Saint-Aubin, France;Institut National de la Recherche Agronomique, Unité Biopolymères, Interactions, Assemblages, 44316 Nantes, France; and.
authors.forename: Pierre
authors.initials: P
authors.lastname: Roblin
authors.affiliation: Department of Medical Biology, University of Tromsø, N-9019 Tromsø, Norway.
authors.forename: Steinar D
authors.initials: SD
authors.lastname: Johansen
authors.affiliation: Architecture et Réactivité de l'ARN, Unité Propre de Recherche 9002, Institut de Biologie Moléculaire et Cellulaire, Université de Strasbourg, Centre National de la Recherche Scientifique, 67084 Strasbourg, France;
authors.forename: Eric
authors.initials: E
authors.lastname: Westhof
authors.affiliation: Architecture et Réactivité de l'ARN, Unité Propre de Recherche 9002, Institut de Biologie Moléculaire et Cellulaire, Université de Strasbourg, Centre National de la Recherche Scientifique, 67084 Strasbourg, France; b.masquida@unistra.fr.
authors.forename: Benoît
authors.initials: B
authors.lastname: Masquida
mesh_terms: D003461:Crystallography; D019143:Evolution, Molecular; D007438:Introns / Q000235:genetics*; D008958:Models, Molecular; D011487:Protein Conformation; D016337:RNA, Catalytic / Q000737:chemistry*; D053838:Scattering, Small Angle; D012641:Selection, Genetic; D015398:Signal Transduction / Q000235:genetics*; D014961:X-Ray Diffraction
chemical_list: D016337:RNA, Catalytic
keywords: GIR1; RNA catalysis; RNA structure; SAXS; crystallography