title: Functional hammerhead ribozymes naturally encoded in the genome of Arabidopsis thaliana.
abstract: The hammerhead ribozyme (HHRz) is an autocatalytic RNA motif found in subviral plant pathogens and transcripts of repetitive DNA sequences in animals. Here, we report the discovery and characterization of unique HHRzs encoded in a plant genome. Two novel sequences were identified on chromosome IV of Arabidopsis thaliana in a database search, which took into account recently defined structural requirements. The HHRzs are expressed in several tissues and coexist in vivo as both cleaved and noncleaved species. In vitro, both sequences cleave efficiently at physiological Mg(2+) concentrations, indicative of functional loop-loop interactions. Kinetic analysis of loop nucleotide variants was used to determine a three-dimensional model of these tertiary interactions. Based on these results, on the lack of infectivity of hammerhead-carrying viroids in Arabidopsis, and on extensive sequence comparisons, we propose that the ribozyme sequences did not invade this plant by horizontal transfer but have evolved independently to perform a specific, yet unidentified, biological function.
authors.affiliation: Arbeitsgruppe Molecular Interactions, Department of Genetics, Universität Kassel, D-34132 Kassel, Germany.
authors.forename: Rita
authors.initials: R
authors.lastname: Przybilski
authors.forename: Stefan
authors.initials: S
authors.lastname: Gräf
authors.forename: Aurélie
authors.initials: A
authors.lastname: Lescoute
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Nellen
authors.forename: Eric
authors.initials: E
authors.lastname: Westhof
authors.forename: Gerhard
authors.initials: G
authors.lastname: Steger
authors.forename: Christian
authors.initials: C
authors.lastname: Hammann
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000821:virology; D001483:Base Sequence / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D018745:Genome, Plant; D008274:Magnesium / Q000378:metabolism; D008958:Models, Molecular; D009711:Nucleotides / Q000235:genetics; D016337:RNA, Catalytic / Q000235:genetics*; D018749:RNA, Plant / Q000235:genetics*; D014772:Viroids / Q000235:genetics
chemical_list: D009711:Nucleotides; D016337:RNA, Catalytic; D018749:RNA, Plant; C427204:hammerhead ribozyme; D008274:Magnesium