Two RNA-binding motifs in eIF3 direct HCV IRES-dependent translation

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• Protein synthesis initiation is a key regulatory process in human biology.
• The 13-subunit eukaryotic translation initiation factor 3 (eIF3) regulates ribosome and mRNA access during initiation through poorly understood mechanisms.

Purpose of the Study:

• To elucidate the structural mechanisms by which eIF3 controls translation initiation.
• To identify the role of specific eIF3 subunits and RNA-binding motifs in HCV IRES-mediated translation.

Main Methods:

• Electron microscopy (EM) for structural analysis.
• Bioinformatics for identifying conserved motifs.
• Biochemical experiments to assess RNA binding and translation activity.

Main Results:

• Two conserved RNA-binding motifs in eIF3 were identified, essential for HCV IRES RNA recognition.
• Mutations in eIF3a's motif impaired eIF3 binding to HCV IRES and the 40S ribosomal subunit, hindering start codon recognition.
• Mutations in eIF3c's motif reduced 40S ribosomal subunit binding and affected downstream initiation steps.

Conclusions:

• This study establishes a direct link between eIF3 structure and HCV IRES RNA start codon recognition.
• The identified RNA-binding motifs in eIF3 are critical for viral translation initiation and likely play roles in the broader human transcriptome.