title: U2-U6 RNA folding reveals a group II intron-like domain and a four-helix junction.
abstract: Intron removal in nuclear precursor mRNA is catalyzed through two transesterification reactions by a multi-megaDalton ribonucleoprotein machine called the spliceosome. A complex between U2 and U6 small nuclear RNAs is a core component of the spliceosome. Here we present an NMR structural analysis of a protein-free U2-U6 complex from Saccharomyces cerevisiae. The observed folding of the U2-U6 complex is a four-helix junction, in which the catalytically important AGC triad base-pairs only within U6 and not with U2. The base-pairing of the AGC triad extends the U6 intramolecular stem-loop (U6 ISL), and the NMR structure of this extended U6 ISL reveals structural similarities with domain 5 of group II self-splicing introns. The observed conformation of the four-helix junction could be relevant to the first, but not the second, step of splicing and may help to position the U6 ISL adjacent to the 5' splice site.
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, Wisconsin 53706, USA.
authors.forename: Dipali G
authors.initials: DG
authors.lastname: Sashital
authors.forename: Gabriel
authors.initials: G
authors.lastname: Cornilescu
authors.forename: C Joel
authors.initials: CJ
authors.lastname: McManus
authors.forename: David A
authors.initials: DA
authors.lastname: Brow
authors.forename: Samuel E
authors.initials: SE
authors.lastname: Butcher
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D007438:Introns; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012326:RNA Splicing; D012342:RNA, Small Nuclear / Q000737:chemistry* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D017381:Spliceosomes / Q000737:chemistry / Q000378:metabolism
chemical_list: D012342:RNA, Small Nuclear; C405484:U2 small nuclear RNA; C405486:U6 small nuclear RNA