Modular assembly of the nucleolar pre-60S ribosomal subunit

Nature. 2018 Apr 5;556(7699):126-129. doi: 10.1038/nature26156. Epub 2018 Mar 5.

Abstract

Early co-transcriptional events during eukaryotic ribosome assembly result in the formation of precursors of the small (40S) and large (60S) ribosomal subunits. A multitude of transient assembly factors regulate and chaperone the systematic folding of pre-ribosomal RNA subdomains. However, owing to a lack of structural information, the role of these factors during early nucleolar 60S assembly is not fully understood. Here we report cryo-electron microscopy (cryo-EM) reconstructions of the nucleolar pre-60S ribosomal subunit in different conformational states at resolutions of up to 3.4 Å. These reconstructions reveal how steric hindrance and molecular mimicry are used to prevent both premature folding states and binding of later factors. This is accomplished by the concerted activity of 21 ribosome assembly factors that stabilize and remodel pre-ribosomal RNA and ribosomal proteins. Among these factors, three Brix-domain proteins and their binding partners form a ring-like structure at ribosomal RNA (rRNA) domain boundaries to support the architecture of the maturing particle. The existence of mutually exclusive conformations of these pre-60S particles suggests that the formation of the polypeptide exit tunnel is achieved through different folding pathways during subsequent stages of ribosome assembly. These structures rationalize previous genetic and biochemical data and highlight the mechanisms that drive eukaryotic ribosome assembly in a unidirectional manner.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Nucleolus / chemistry*
  • Cross-Linking Reagents / chemistry
  • Cryoelectron Microscopy*
  • Models, Molecular
  • Molecular Mimicry
  • Protein Domains
  • Protein Stability
  • RNA Folding
  • RNA, Ribosomal / chemistry
  • RNA, Ribosomal / genetics
  • RNA, Ribosomal / metabolism
  • RNA, Ribosomal / ultrastructure
  • Reproducibility of Results
  • Ribosomal Proteins / chemistry
  • Ribosomal Proteins / metabolism
  • Ribosomal Proteins / ultrastructure
  • Ribosome Subunits, Large, Eukaryotic / chemistry
  • Ribosome Subunits, Large, Eukaryotic / metabolism*
  • Ribosome Subunits, Large, Eukaryotic / ultrastructure*
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / metabolism
  • Saccharomyces cerevisiae Proteins / ultrastructure
  • Saccharomyces cerevisiae* / chemistry
  • Saccharomyces cerevisiae* / genetics
  • Saccharomyces cerevisiae* / ultrastructure

Substances

  • Cross-Linking Reagents
  • Erb1 protein, S cerevisiae
  • RNA, Ribosomal
  • Ribosomal Proteins
  • Saccharomyces cerevisiae Proteins
  • RNA, ribosomal, 25S