title: Unusual metal specificity and structure of the group I ribozyme from Chlamydomonas reinhardtii 23S rRNA.
abstract: Group I intron ribozymes require cations for folding and catalysis, and the current literature indicates that a number of cations can promote folding, but only Mg2+ and Mn2+ support both processes. However, some group I introns are active only with Mg2+, e.g. three of the five group I introns in Chlamydomonas reinhardtii. We have investigated one of these ribozymes, an intron from the 23S LSU rRNA gene of Chlamydomonas reinhardtii (Cr.LSU), by determining if the inhibition by Mn2+ involves catalysis, folding, or both. Kinetic analysis of guanosine-dependent cleavage by a Cr.LSU ribozyme, 23S.5 Delta Gb, that lacks the 3' exon and intron-terminal G shows that Mn2+ does not affect guanosine binding or catalysis, but instead promotes misfolding of the ribozyme. Surprisingly, ribozyme misfolding induced by Mn2+ is highly cooperative, with a Hill coefficient larger than that of native folding induced by Mg2+. At lower Mn2+ concentrations, metal inhibition is largely alleviated by the guanosine cosubstrate (GMP). The concentration dependence of guanosine cosubstrate-induced folding suggests that it functions by interacting with the G binding site, perhaps by displacing an inhibitory Mn2+. Because of these and other properties of Cr.LSU, the tertiary structure of the intron from 23S.5 Delta Gb was examined using Fe2+-EDTA cleavage. The ground-state structure shows evidence of an unusually open ribozyme core: the catalytic P3-P7 domain and the nucleotides that connect it to the P4-P5-P6 domain are exposed to solvent. The implications of this structure for the in vitro and in vivo properties of this intron ribozyme are discussed.
authors.affiliation: Department of Biochemistry, Tapei Medical University, Taiwan.
authors.forename: Tai-Chih
authors.initials: TC
authors.lastname: Kuo
authors.forename: Obed W
authors.initials: OW
authors.lastname: Odom
authors.forename: David L
authors.initials: DL
authors.lastname: Herrin
mesh_terms: D000818:Animals; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D007438:Introns; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D008954:Models, Biological; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016337:RNA, Catalytic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012338:RNA, Ribosomal, 23S / Q000235:genetics*; D044563:RNA, Ribosomal, Self-Splicing / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: C116167:GIR1 ribozyme; D016337:RNA, Catalytic; D012338:RNA, Ribosomal, 23S; D044563:RNA, Ribosomal, Self-Splicing; D008345:Manganese; D008274:Magnesium