title: Molecular architecture of the 90S small subunit pre-ribosome.
abstract: Eukaryotic small ribosomal subunits are first assembled into 90S pre-ribosomes. The complete 90S is a gigantic complex with a molecular mass of approximately five megadaltons. Here, we report the nearly complete architecture ofSaccharomyces cerevisiae90S determined from three cryo-electron microscopy single particle reconstructions at 4.5 to 8.7 angstrom resolution. The majority of the density maps were modeled and assigned to specific RNA and protein components. The nascent ribosome is assembled into isolated native-like substructures that are stabilized by abundant assembly factors. The 5' external transcribed spacer and U3 snoRNA nucleate a large subcomplex that scaffolds the nascent ribosome. U3 binds four sites of pre-rRNA, including a novel site on helix 27 but not the 3' side of the central pseudoknot, and crucially organizes the 90S structure. The 90S model provides significant insight into the principle of small subunit assembly and the function of assembly factors.
authors.affiliation: PTN Joint Graduate Program, School of Life Sciences, Tsinghua University, Beijing, China.|Key Laboratory of RNA Biology, Institute of Biophysics, CAS Center for Excellence in Biomacromolecules, Chinese Academy of Sciences, Beijing, China.|National Institute of Biological Sciences, Beijing, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Sun
authors.affiliation: Key Laboratory of RNA Biology, Institute of Biophysics, CAS Center for Excellence in Biomacromolecules, Chinese Academy of Sciences, Beijing, China.
authors.forename: Xing
authors.identifier: 0000-0003-4839-4857
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Key Laboratory of RNA Biology, Institute of Biophysics, CAS Center for Excellence in Biomacromolecules, Chinese Academy of Sciences, Beijing, China.|National Institute of Biological Sciences, Beijing, China.|Department of Biochemistry and Molecular Biology, College of Life Sciences, Beijing Normal University, Beijing, China.
authors.forename: Jia
authors.initials: J
authors.lastname: Qi
authors.affiliation: Key Laboratory of RNA Biology, Institute of Biophysics, CAS Center for Excellence in Biomacromolecules, Chinese Academy of Sciences, Beijing, China.|National Institute of Biological Sciences, Beijing, China.|College of Biological Sciences, China Agricultural University, Beijing, China.
authors.forename: Weidong
authors.initials: W
authors.lastname: An
authors.affiliation: National Institute of Biological Sciences, Beijing, China.
authors.forename: Pengfei
authors.initials: P
authors.lastname: Lan
authors.affiliation: National Institute of Biological Sciences, Beijing, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Tan
authors.affiliation: Key Laboratory of RNA Biology, Institute of Biophysics, CAS Center for Excellence in Biomacromolecules, Chinese Academy of Sciences, Beijing, China.
authors.forename: Rongchang
authors.initials: R
authors.lastname: Chen
authors.affiliation: Key Laboratory of RNA Biology, Institute of Biophysics, CAS Center for Excellence in Biomacromolecules, Chinese Academy of Sciences, Beijing, China.|National Institute of Biological Sciences, Beijing, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.affiliation: National Institute of Biological Sciences, Beijing, China.
authors.forename: Sanduo
authors.initials: S
authors.lastname: Zheng
authors.affiliation: National Institute of Biological Sciences, Beijing, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhang
authors.affiliation: National Institute of Biological Sciences, Beijing, China.
authors.forename: Xining
authors.initials: X
authors.lastname: Chen
authors.affiliation: National Institute of Biological Sciences, Beijing, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: PTN Joint Graduate Program, School of Life Sciences, Tsinghua University, Beijing, China.|Key Laboratory of RNA Biology, Institute of Biophysics, CAS Center for Excellence in Biomacromolecules, Chinese Academy of Sciences, Beijing, China.|National Institute of Biological Sciences, Beijing, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Chen
authors.affiliation: National Institute of Biological Sciences, Beijing, China.
authors.forename: Meng-Qiu
authors.identifier: 0000-0002-6094-1182
authors.initials: MQ
authors.lastname: Dong
authors.affiliation: Key Laboratory of RNA Biology, Institute of Biophysics, CAS Center for Excellence in Biomacromolecules, Chinese Academy of Sciences, Beijing, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Keqiong
authors.identifier: 0000-0001-6169-7049
authors.initials: K
authors.lastname: Ye
mesh_terms: D020285:Cryoelectron Microscopy; D007091:Image Processing, Computer-Assisted; D012270:Ribosomes / Q000648:ultrastructure*; D012441:Saccharomyces cerevisiae / Q000648:ultrastructure*
keywords: 90S pre-ribosome; S. cerevisiae; biophysics; cryo-EM; ribosome assembly; structural biology