title: Structure of the Tetrahymena ribozyme: base triple sandwich and metal ion at the active site.
abstract: The Tetrahymena intron is an RNA catalyst, or ribozyme. As part of its self-splicing reaction, this ribozyme catalyzes phosphoryl transfer between guanosine and a substrate RNA strand. Here we report the refined crystal structure of an active Tetrahymena ribozyme in the absence of its RNA substrate at 3.8 A resolution. The 3'-terminal guanosine (omegaG), which serves as the attacking group for RNA cleavage, forms a coplanar base triple with the G264-C311 base pair, and this base triple is sandwiched by three other base triples. In addition, a metal ion is present in the active site, contacting or positioned close to the ribose of the omegaG and five phosphates. All of these phosphates have been shown to be important for catalysis. Therefore, we provide a picture of how the ribozyme active site positions both a catalytic metal ion and the nucleophilic guanosine for catalysis prior to binding its RNA substrate.
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Guo
authors.forename: Anne R
authors.initials: AR
authors.lastname: Gooding
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Cech
mesh_terms: D000818:Animals; D020029:Base Pairing; D001483:Base Sequence; D001665:Binding Sites; D002384:Catalysis; D006151:Guanosine / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010710:Phosphates / Q000378:metabolism*; D016337:RNA, Catalytic / Q000737:chemistry* / Q000378:metabolism; D016053:RNA, Protozoan; D013379:Substrate Specificity; D013768:Tetrahymena / Q000201:enzymology*
chemical_list: C116167:GIR1 ribozyme; D010710:Phosphates; D016337:RNA, Catalytic; D016053:RNA, Protozoan; D006151:Guanosine; D008274:Magnesium