title: The architecture of the spliceosomal U4/U6.U5 tri-snRNP.
abstract: U4/U6.U5 tri-snRNP is a 1.5-megadalton pre-assembled spliceosomal complex comprising U5 small nuclear RNA (snRNA), extensively base-paired U4/U6 snRNAs and more than 30 proteins, including the key components Prp8, Brr2 and Snu114. The tri-snRNP combines with a precursor messenger RNA substrate bound to U1 and U2 small nuclear ribonucleoprotein particles (snRNPs), and transforms into a catalytically active spliceosome after extensive compositional and conformational changes triggered by unwinding of the U4 and U6 (U4/U6) snRNAs. Here we use cryo-electron microscopy single-particle reconstruction of Saccharomyces cerevisiae tri-snRNP at 5.9 Å resolution to reveal the essentially complete organization of its RNA and protein components. The single-stranded region of U4 snRNA between its 3' stem-loop and the U4/U6 snRNA stem I is loaded into the Brr2 helicase active site ready for unwinding. Snu114 and the amino-terminal domain of Prp8 position U5 snRNA to insert its loop I, which aligns the exons for splicing, into the Prp8 active site cavity. The structure provides crucial insights into the activation process and the active site of the spliceosome.
authors.affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Thi Hoang Duong
authors.initials: TH
authors.lastname: Nguyen
authors.affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Wojciech P
authors.initials: WP
authors.lastname: Galej
authors.affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Xiao-chen
authors.initials: XC
authors.lastname: Bai
authors.affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Christos G
authors.initials: CG
authors.lastname: Savva
authors.affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Newman
authors.affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Sjors H W
authors.initials: SH
authors.lastname: Scheres
authors.affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Nagai
mesh_terms: D001665:Binding Sites; D020285:Cryoelectron Microscopy; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D020365:RNA Helicases / Q000737:chemistry / Q000378:metabolism; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000737:chemistry* / Q000378:metabolism; D017415:Ribonucleoprotein, U5 Small Nuclear / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism; D017381:Spliceosomes / Q000737:chemistry / Q000502:physiology*
chemical_list: C077018:PRP8 protein, S cerevisiae; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D017415:Ribonucleoprotein, U5 Small Nuclear; C472240:SNU114 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C104158:BRR2 protein, S cerevisiae; D020365:RNA Helicases