title: Structure of a yeast catalytic step I spliceosome at 3.4 Å resolution.
abstract: Each cycle of pre-messenger RNA splicing, carried out by the spliceosome, comprises two sequential transesterification reactions, which result in the removal of an intron and the joining of two exons. Here we report an atomic structure of a catalytic step I spliceosome (known as the C complex) from Saccharomyces cerevisiae, as determined by cryo-electron microscopy at an average resolution of 3.4 angstroms. In the structure, the 2'-OH of the invariant adenine nucleotide in the branch point sequence (BPS) is covalently joined to the phosphate at the 5' end of the 5' splice site (5'SS), forming an intron lariat. The freed 5' exon remains anchored to loop I of U5 small nuclear RNA (snRNA), and the 5'SS and BPS of the intron form duplexes with conserved U6 and U2 snRNA sequences, respectively. Specific placement of these RNA elements at the catalytic cavity of Prp8 is stabilized by 15 protein components, including Snu114 and the splicing factors Cwc21, Cwc22, Cwc25, and Yju2. These features, representing the conformation of the spliceosome after the first-step reaction, predict structural changes that are needed for the execution of the second-step transesterification reaction.
authors.affiliation: Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Ruixue
authors.initials: R
authors.lastname: Wan
authors.affiliation: Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Chuangye
authors.initials: C
authors.lastname: Yan
authors.affiliation: Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Bai
authors.affiliation: Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Gaoxingyu
authors.initials: G
authors.lastname: Huang
authors.affiliation: Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China. shi-lab@tsinghua.edu.cn.
authors.forename: Yigong
authors.initials: Y
authors.lastname: Shi
mesh_terms: D000227:Adenine Nucleotides / Q000737:chemistry; D055162:Biocatalysis; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics; D020285:Cryoelectron Microscopy; D005091:Exons; D007438:Introns; D008956:Models, Chemical; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics; D000072417:Protein Domains; D022821:RNA Splice Sites; D012326:RNA Splicing; D000072260:RNA Splicing Factors / Q000737:chemistry* / Q000235:genetics; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics; D017381:Spliceosomes / Q000737:chemistry* / Q000235:genetics
chemical_list: D000227:Adenine Nucleotides; C555352:CWC22 protein, S cerevisiae; D002352:Carrier Proteins; C545658:Cwc21 protein, S cerevisiae; C544745:Cwc25 protein, S cerevisiae; D009687:Nuclear Proteins; D022821:RNA Splice Sites; D000072260:RNA Splicing Factors; D012342:RNA, Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; C405484:U2 small nuclear RNA; C405485:U5 small nuclear RNA; C075469:YJU2 protein, S cerevisiae