title: Visualizing group II intron catalysis through the stages of splicing.
abstract: Group II introns are self-splicing ribozymes that share a reaction mechanism and a common ancestor with the eukaryotic spliceosome, thereby providing a model system for understanding the chemistry of pre-mRNA splicing. Here we report 14 crystal structures of a group II intron at different stages of catalysis. We provide a detailed mechanism for the first step of splicing, we describe a reversible conformational change between the first and the second steps of splicing, and we present the ligand-free intron structure after splicing in an active state that corresponds to the retrotransposable form of the intron. During each reaction, the reactants are aligned and activated by a heteronuclear four-metal-ion center that contains a metal cluster and obligate monovalent cations, and they adopt a structural arrangement similar to that of protein endonucleases. Based on our data, we propose a model for the splicing cycle and show that it is applicable to the eukaryotic spliceosome.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06511, USA.
authors.forename: Marco
authors.initials: M
authors.lastname: Marcia
authors.forename: Anna Marie
authors.initials: AM
authors.lastname: Pyle
mesh_terms: D001406:Bacillaceae / Q000235:genetics*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D007438:Introns; D008954:Models, Biological; D009154:Mutation; D012322:RNA Precursors / Q000737:chemistry / Q000378:metabolism; D022821:RNA Splice Sites; D012326:RNA Splicing; D012329:RNA, Bacterial / Q000737:chemistry* / Q000378:metabolism; D018626:Retroelements
chemical_list: D012322:RNA Precursors; D022821:RNA Splice Sites; D012329:RNA, Bacterial; D018626:Retroelements