title: The 3.8 Å structure of the U4/U6.U5 tri-snRNP: Insights into spliceosome assembly and catalysis.
abstract: Splicing of precursor messenger RNA is accomplished by a dynamic megacomplex known as the spliceosome. Assembly of a functional spliceosome requires a preassembled U4/U6.U5 tri-snRNP complex, which comprises the U5 small nuclear ribonucleoprotein (snRNP), the U4 and U6 small nuclear RNA (snRNA) duplex, and a number of protein factors. Here we report the three-dimensional structure of a Saccharomyces cerevisiae U4/U6.U5 tri-snRNP at an overall resolution of 3.8 angstroms by single-particle electron cryomicroscopy. The local resolution for the core regions of the tri-snRNP reaches 3.0 to 3.5 angstroms, allowing construction of a refined atomic model. Our structure contains U5 snRNA, the extensively base-paired U4/U6 snRNA, and 30 proteins including Prp8 and Snu114, which amount to 8495 amino acids and 263 nucleotides with a combined molecular mass of ~1 megadalton. The catalytic nucleotide U80 from U6 snRNA exists in an inactive conformation, stabilized by its base-pairing interactions with U4 snRNA and protected by Prp3. Pre-messenger RNA is bound in the tri-snRNP through base-pairing interactions with U6 snRNA and loop I of U5 snRNA. This structure, together with that of the spliceosome, reveals the molecular choreography of the snRNAs in the activation process of the spliceosomal ribozyme.
authors.affiliation: Ministry of Education Key Laboratory of Protein Science, Tsinghua-Peking Joint Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Ruixue
authors.initials: R
authors.lastname: Wan
authors.affiliation: Ministry of Education Key Laboratory of Protein Science, Tsinghua-Peking Joint Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Chuangye
authors.initials: C
authors.lastname: Yan
authors.affiliation: Ministry of Education Key Laboratory of Protein Science, Tsinghua-Peking Joint Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Bai
authors.affiliation: Ministry of Education Key Laboratory of Protein Science, Tsinghua-Peking Joint Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.affiliation: National Center for Protein Science Shanghai, Institute of Biochemistry and Cell Biology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Min
authors.initials: M
authors.lastname: Huang
authors.affiliation: National Center for Protein Science Shanghai, Institute of Biochemistry and Cell Biology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Catherine C L
authors.initials: CC
authors.lastname: Wong
authors.affiliation: Ministry of Education Key Laboratory of Protein Science, Tsinghua-Peking Joint Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Yigong
authors.initials: Y
authors.lastname: Shi
mesh_terms: D002384:Catalysis; D020285:Cryoelectron Microscopy; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D012322:RNA Precursors / Q000737:chemistry; D012326:RNA Splicing; D012333:RNA, Messenger / Q000737:chemistry; D012342:RNA, Small Nuclear / Q000737:chemistry* / Q000648:ultrastructure; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000737:chemistry* / Q000648:ultrastructure; D017415:Ribonucleoprotein, U5 Small Nuclear / Q000737:chemistry* / Q000648:ultrastructure; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000648:ultrastructure; D017381:Spliceosomes / Q000737:chemistry* / Q000648:ultrastructure
chemical_list: D012322:RNA Precursors; D012333:RNA, Messenger; D012342:RNA, Small Nuclear; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D017415:Ribonucleoprotein, U5 Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; C405482:U4 small nuclear RNA; C405485:U5 small nuclear RNA; C405486:U6 small nuclear RNA