title: Stepwise and dynamic assembly of the earliest precursors of small ribosomal subunits in yeast.
abstract: The eukaryotic ribosomal RNA (rRNA) is associated cotranscriptionally with numerous factors into an enormous 90S preribosomal particle that conducts early processing of small ribosomal subunits. The assembly pathway and structure of the 90S particle is poorly understood. Here, we affinity-purified and analyzed the constituents of yeast 90S particles that were assembled on a series of plasmid-encoded 3'-truncated pre-18S RNAs. We determined the assembly point of 65 proteins and the U3, U14, and snR30 small nucleolar RNAs (snoRNAs), revealing a stepwise and dynamic assembly map. The 5' external transcribed spacer (ETS) alone can nucleate a large complex. When the 18S rRNA is nearly complete, the 90S structure undergoes a dramatic reorganization, releasing U14, snR30, and 14 protein factors that bind earlier. We also identified a reference state of 90S that is fully assembled yet has not undergone 5'ETS processing. The assembly map present here provides a new framework to understand small subunit biogenesis.
authors.affiliation: National Institute of Biological Sciences, Beijing, Beijing 102206, China;
authors.forename: Liman
authors.initials: L
authors.lastname: Zhang
authors.affiliation: National Institute of Biological Sciences, Beijing, Beijing 102206, China; College of Biological Sciences, China Agricultural University, Beijing 100193, China; Key Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; Beijing Key Laboratory of Noncoding RNA, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Chen
authors.initials: C
authors.lastname: Wu
authors.affiliation: National Institute of Biological Sciences, Beijing, Beijing 102206, China;
authors.forename: Gaihong
authors.initials: G
authors.lastname: Cai
authors.affiliation: National Institute of Biological Sciences, Beijing, Beijing 102206, China;
authors.forename: She
authors.initials: S
authors.lastname: Chen
authors.affiliation: Key Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; Beijing Key Laboratory of Noncoding RNA, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Keqiong
authors.identifier: http://orcid.org/0000-0001-6169-7049
authors.initials: K
authors.lastname: Ye
mesh_terms: D002875:Chromosomes / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012322:RNA Precursors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D012337:RNA, Ribosomal, 18S / Q000235:genetics / Q000378:metabolism; D020537:RNA, Small Nucleolar / Q000378:metabolism; D054682:Ribosome Subunits, Small, Eukaryotic / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*
chemical_list: D021903:DNA, Ribosomal Spacer; D012322:RNA Precursors; D012337:RNA, Ribosomal, 18S; D020537:RNA, Small Nucleolar
keywords: 90S preribosome; mass spectrometry; ribosome assembly; small nucleolar RNA