title: The K-loop, a general feature of the Pyrococcus C/D guide RNAs, is an RNA structural motif related to the K-turn.
abstract: The C/D guide RNAs predicted from the genomic sequences of three species of Pyrococcus delineate a family of small non-coding archaeal RNAs involved in the methylation of rRNA and tRNA. The C/D guides assemble into ribonucleoprotein (RNP) that contains the methyltransferase. The protein L7Ae, a key structural component of the RNP, binds to a Kink-turn (K-turn) formed by the C/D motif. The K-turn is a structure that consists of two RNA stems separated by a short asymmetric loop with a characteristic sharp bend (kink) between the two stems. The majority of the pyrococcal C/D guides contain a short 3 nt-spacer between the C'/D' motifs. We show here that conserved terminal stem-loops formed by the C'/D' motif of the Pyrococcus C/D RNAs are also L7Ae-binding sites. These stem-loops are related to the K-turn by sequence and structure, but they consist of a single stem closed by a terminal loop. We have named this structure the K-loop. We show that conserved non-canonical base pairs in the stem of the K-loop are necessary for L7Ae binding. For the C/D guides with a 3 nt-spacer we show that the sequence and length is also important. The K-loop could improve the stability of the C/D guide RNAs in Pyrococcal species, which are extreme hyperthermophiles.
authors.affiliation: Laboratoire de Microbiologie et Génétique Moléculaires, Centre National de la Recherche Scientifique, UMR 5100 Université Paul Sabatier 118 route de Narbonne, 31062 Toulouse cedex 9, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Nolivos
authors.forename: Agamemnon J
authors.initials: AJ
authors.lastname: Carpousis
authors.forename: Béatrice
authors.initials: B
authors.lastname: Clouet-d'Orval
mesh_terms: D019843:Archaeal Proteins / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D019711:Pyrococcus / Q000235:genetics*; D019642:RNA, Archaeal / Q000737:chemistry* / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism; D058727:RNA, Small Untranslated
chemical_list: D019843:Archaeal Proteins; D019642:RNA, Archaeal; D012261:Ribonucleoproteins; D058727:RNA, Small Untranslated