Distribution and structural diversity of Type IV internal ribosome entry sites

Area of Science:

• Molecular Biology
• Virology
• RNA Biology

Background:

• Internal Ribosome Entry Sites (IRESs) are RNA elements enabling cap-independent translation initiation in eukaryotes.
• Type IV IRESs, exemplified by the hepatitis C virus IRES, interact directly with the 40S ribosomal subunit and require fewer initiation factors.

Purpose of the Study:

• To comprehensively identify and classify the architectural diversity of Type IV IRESs.
• To understand the evolutionary distribution and structural variations within this class of IRESs.

Main Methods:

• A homology-based search using secondary structure models identified 163 putative Type IV IRESs.
• Clustering analysis grouped IRESs based on secondary structure elements.
• Chemical probing and in vitro translation assays validated structures and assessed function.

Main Results:

• 163 putative Type IV IRESs were identified across diverse viral hosts and phylogenies.
• Three distinct clusters emerged based on secondary structure variations (expansions and deletions).
• Structural differences were confirmed and shown to correlate with functional variations in translation assays.

Conclusions:

• This study reveals significant architectural diversity within Type IV IRESs.
• Identified structural adaptations may influence the mechanism and function of these RNA elements.
• The findings expand our understanding of viral translation strategies and RNA element evolution.