title: A second divalent metal ion in the group II intron reaction center.
abstract: Group II introns are mobile genetic elements that have been implicated as agents of genetic diversity, and serve as important model systems for investigating RNA catalysis and pre-mRNA splicing. In the absence of an atomic-resolution structure of the intron, detailed understanding of its catalytic mechanism has remained elusive. Previous identification of a divalent metal ion stabilizing the leaving group in both splicing steps suggested that the group II intron may employ a "two-metal ion" mechanism, a catalytic strategy used by a number of protein phosphoester transfer enzymes. Using metal rescue experiments, we now reveal the presence of a second metal ion required for nucleophile activation in the exon-ligation step of group II intron splicing. Coupled with biochemical and structural evidence of at least two metal ions at the group I intron reaction center, these results suggest a mechanistic paradigm for describing catalysis by large ribozymes.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Gordon
authors.forename: Robert
authors.initials: R
authors.lastname: Fong
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Piccirilli
mesh_terms: D001665:Binding Sites; D002413:Cations, Divalent; D005091:Exons; D007438:Introns; D008274:Magnesium / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D012326:RNA Splicing; D016337:RNA, Catalytic / Q000737:chemistry* / Q000235:genetics; D013379:Substrate Specificity; D013455:Sulfur / Q000737:chemistry
chemical_list: D002413:Cations, Divalent; D016337:RNA, Catalytic; D013455:Sulfur; D008274:Magnesium; D010100:Oxygen