rRNA expansion segment 7 in eukaryotes: from Signature Fold to tentacles

Area of Science:

• Ribosome biogenesis and evolution
• RNA structure and dynamics
• Eukaryotic molecular biology

Background:

• Ribosomal core structure is conserved, but eukaryotic ribosomes possess variable rRNA expansion segments (ESs).
• Expansion segment 7 (ES7) shows significant diversity across eukaryotes, with lengths varying greatly.
• Understanding ES7 evolution provides insights into ribosomal structural diversification.

Purpose of the Study:

• To determine the 3D structures of ES7 across eukaryotic diversity.
• To elucidate the evolutionary pathways of ES7 development.
• To model the atomic-level accretion of rRNA growth within ES7.

Main Methods:

• Analysis of experimental 3D structures and phylogenetic relationships.
• Multiple sequence alignments and RNA folding algorithms.
• 3D modeling using RNAComposer and the accretion model of ribosomal evolution.

Main Results:

• The 'ES7 Signature Fold' is a conserved motif in both 2D topology and 3D structure across eukaryotic ribosomes.
• ES7 evolved through incremental, recursive growth events, supporting an atomic-level accretion model.
• Convergent evolution likely contributed to the distribution of certain ES7 features.

Conclusions:

• The ES7 Signature Fold provides a stable framework for rRNA expansion.
• Ribosomal expansion segments evolve via accretion, with potential for convergent acquisition.
• The study successfully modeled the complete LSU rRNA structure of Mus musculus.