A complex IRES at the 5'-UTR of a viral mRNA assembles a functional 48S complex via an uAUG intermediate

Area of Science:

• Molecular Biology
• Virology
• Structural Biology

Background:

• Viruses require host cell protein production machinery for replication.
• Viral strategies include ribosome hijacking and cellular mimicry.
• Translation initiation is a key regulatory step targeted by viruses.

Purpose of the Study:

• To characterize a novel Internal Ribosomal Entry Site (IRES) from a viral 5 on-translated region (5 -UTR).
• To elucidate the mechanism of translation initiation complex assembly mediated by this IRES.
• To understand the role of viral IRES structures in eukaryotic translation regulation.

Main Methods:

• Electron cryo-microscopy (cryo-EM) for structural determination.
• Reconstituted translation initiation assays using native cellular components.
• Biochemical and biophysical characterization of RNA-protein interactions.

Main Results:

• A novel IRES with an extended, multi-domain architecture was identified.
• The IRES was shown to assemble a functional translation initiation complex via an upstream AUG (uAUG) intermediate.
• Structural data revealed the IRES encircles the 40S ribosomal subunit head.

Conclusions:

• Viral IRESs represent a diverse and important mechanism for controlling gene expression.
• The 5 -UTR plays a critical role in regulating translation.
• Understanding viral IRES structure and function offers insights into translation regulation and potential antiviral targets.