Assembly of the Bacterial Ribosome with Circularly Permuted rRNA

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Co-transcriptional assembly is vital for RNA-protein complex formation, including translation machinery.
• Bacterial ribosome synthesis involves the large ribosomal subunit (LSU).
• Previous studies suggested flexibility in the transcription order of rRNA domains.

Approach:

• Utilized cryo-electron microscopy (cryo-EM) to analyze ribosome intermediates.
• Studied *in vitro* ribosome synthesis using circularly permuted (CiPer) rRNAs.
• Resolved twenty-three distinct LSU intermediates to map assembly pathways.

Key Points:

• Identified conserved assembly routes and hierarchical organization of assembly blocks.
• Circular permutation revealed intricate interdependencies in rRNA helix formation.
• Demonstrated that while rRNA domain synthesis order is flexible, domain association follows a specific sequence.

Conclusions:

• The assembly hierarchy of the bacterial LSU is robust and conserved.
• Specific order of domain association is critical for efficient ribosome biogenesis, driven by evolutionary pressure.
• This study provides a coherent framework for understanding CiPer rRNA assembly within the established hierarchy.