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The complete structure of the small-subunit processome.

Jonas Barandun1, Malik Chaker-Margot1,2, Mirjam Hunziker1

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Summary
This summary is machine-generated.

The earliest precursor to the eukaryotic small ribosomal subunit, the small-subunit processome, has been structurally revealed. This cryo-EM study uncovers its molecular architecture and assembly mechanisms.

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Area of Science:

  • Molecular Biology
  • Structural Biology
  • Biochemistry

Background:

  • The small-subunit processome is a crucial precursor in eukaryotic ribosome biogenesis.
  • Understanding its structure is key to deciphering early ribosome assembly steps.
  • Previous structural data on this dynamic assembly has been limited.

Purpose of the Study:

  • To determine the near-atomic structure of the Saccharomyces cerevisiae small-subunit processome.
  • To elucidate the molecular mechanisms governing early ribosome subunit formation.
  • To identify the roles of ribosome-assembly factors and RNA in this process.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) was employed to resolve the processome structure.
  • High-resolution structural analysis provided a detailed model of the assembly.
  • Biochemical and biophysical techniques were used to understand molecular interactions.

Main Results:

  • A near-atomic model (3.8 Å resolution) of the small-subunit processome was obtained.
  • The structure reveals 51 ribosome-assembly factors and two RNAs encapsulating the pre-18S rRNA and 15 ribosomal proteins.
  • Mechanisms including molecular mimicry, steric hindrance, and RNA remodeling prevent premature folding of key rRNA structures.

Conclusions:

  • The study provides unprecedented structural insights into the earliest stage of small ribosomal subunit biogenesis.
  • Flexible proteins play a significant role in connecting distant structural elements within the processome.
  • The findings reveal a sophisticated interplay of factors ensuring accurate ribosome assembly.