HCV IRES Captures an Actively Translating 80S Ribosome

Area of Science:

• Molecular Biology
• Virology
• Structural Biology

Background:

• Hepatitis C virus (HCV) relies on an internal ribosome entry site (IRES) for translation initiation.
• Understanding the mechanism of HCV IRES-mediated translation is crucial for developing antiviral strategies.

Purpose of the Study:

• To elucidate the structural basis of HCV IRES binding to the ribosome during translation initiation.
• To investigate the interaction between the HCV IRES and both cap-dependent and IRES-dependent translating ribosomes.

Main Methods:

• Cryoelectron microscopy (cryo-EM) to determine high-resolution structures.
• Biochemical experiments to assess ribosome-IRES interactions and translation efficiency.

Main Results:

• Cryo-EM revealed HCV IRES binding to the 40S ribosomal subunit on the solvent side of cap-dependent translating 80S ribosomes.
• Structures of IRES-bound 40S subunits show the IRES 'body' (domain III) interacting with the 40S subunit, while the 'long arm' (domain II) remains flexible.
• Biochemical data indicate that translating ribosomes are preferred substrates for HCV IRES over free ribosomes.

Conclusions:

• The HCV IRES efficiently binds to and utilizes translating ribosomes for initiation.
• This interaction facilitates rapid translation initiation on downstream mRNA as soon as ongoing translation finishes.
• The findings provide structural insights into a unique viral translation mechanism.