title: Multiple tertiary interactions involving domain II of group II self-splicing introns.
abstract: The ribozyme core of group II introns is organized into six domains of secondary structure. Of these, domain II was long thought to be relatively unimportant for group II self-splicing. However, we now demonstrate the existence, in both major subdivisions of the group II family, of essential tertiary interactions involving domain II. theta-theta' is a novel tertiary interaction between the terminal loop of the IC1 stem of domain I and the basal stem of domain II. The theta-theta' interaction appears to stabilize the group II ribozyme core: it is essential for efficient self-splicing at elevated temperatures but, as shown by the use of a bimolecular reaction system, molecules with a defective theta-theta' contact are not affected in catalysis. An interaction, eta-eta', between domains II and VI of subgroup IIB introns was recently reported to mediate a conformational rearrangement between the two steps of the self-splicing reaction. We now show that domains II and VI of subgroup IIA introns also contact each other, although in a somewhat different way. Reinforcement of the eta-eta' interaction of a subgroup IIA intron prevents the use of a specific 2'-hydroxyl group in domain VI to initiate splicing by transesterification at the 5' splice site; the 5' intron-exon junction is hydrolyzed instead. Since disruption of eta-eta' has exactly opposite effects, and promotes reversal of the first transesterification step, it is concluded that formation of eta-eta' mediates a conformational change in subgroup IIA introns as well. Just like the eta-eta' interaction of subgroup IIB introns, the eta-eta' interaction of subgroup IIA introns (and the theta-theta' interaction) involves terminal loops of the GNRA family and their RNA receptors. Therefore, these motifs are used by nature not only to stabilize three-dimensional RNA architectures, but also in situations that require dynamic interactions.
authors.affiliation: Centre de Génétique Moléculaire du CNRS, Gif-sur-Yvette, France.
authors.forename: M
authors.initials: M
authors.lastname: Costa
authors.forename: E
authors.initials: E
authors.lastname: Déme
authors.forename: A
authors.initials: A
authors.lastname: Jacquier
authors.forename: F
authors.initials: F
authors.lastname: Michel
mesh_terms: D001483:Base Sequence; D003576:Electron Transport Complex IV / Q000235:genetics; D007438:Introns / Q000235:genetics*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D012326:RNA Splicing / Q000235:genetics*; D012333:RNA, Messenger / Q000737:chemistry* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics
chemical_list: D012333:RNA, Messenger; D003576:Electron Transport Complex IV