title: Organization of core spliceosomal components U5 snRNA loop I and U4/U6 Di-snRNP within U4/U6.U5 Tri-snRNP as revealed by electron cryomicroscopy.
abstract: In eukaryotes, pre-mRNA exons are interrupted by large noncoding introns. Alternative selection of exons and nucleotide-exact removal of introns are performed by the spliceosome, a highly dynamic macromolecular machine. U4/U6.U5 tri-snRNP is the largest and most conserved building block of the spliceosome. By 3D electron cryomicroscopy and labeling, the exon-aligning U5 snRNA loop I is localized at the center of the tetrahedrally shaped tri-snRNP reconstructed to approximately 2.1 nm resolution in vitrified ice. Independent 3D reconstructions of its subunits, U4/U6 and U5 snRNPs, show how U4/U6 and U5 combine to form tri-snRNP and, together with labeling experiments, indicate a close proximity of the spliceosomal core components U5 snRNA loop I and U4/U6 at the center of tri-snRNP. We suggest that this central tri-snRNP region may be the site to which the prespliceosomal U2 snRNA has to approach closely during formation of the catalytic core of the spliceosome.
authors.affiliation: Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
authors.forename: Bjoern
authors.initials: B
authors.lastname: Sander
authors.forename: Monika M
authors.initials: MM
authors.lastname: Golas
authors.forename: Evgeny M
authors.initials: EM
authors.lastname: Makarov
authors.forename: Hero
authors.initials: H
authors.lastname: Brahms
authors.forename: Berthold
authors.initials: B
authors.lastname: Kastner
authors.forename: Reinhard
authors.initials: R
authors.lastname: Lührmann
authors.forename: Holger
authors.initials: H
authors.lastname: Stark
mesh_terms: D001483:Base Sequence; D020134:Catalytic Domain; D020285:Cryoelectron Microscopy / Q000379:methods*; D005091:Exons; D006367:HeLa Cells; D006801:Humans; D021621:Imaging, Three-Dimensional; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D012342:RNA, Small Nuclear / Q000737:chemistry*; D017381:Spliceosomes / Q000737:chemistry / Q000648:ultrastructure*
chemical_list: D012342:RNA, Small Nuclear; C405482:U4 small nuclear RNA; C405485:U5 small nuclear RNA; C405486:U6 small nuclear RNA