Cellular cap-binding protein, eIF4E, promotes picornavirus genome restructuring and translation

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• Picornaviruses utilize internal ribosome entry sites (IRESs) for cap-independent translation.
• IRESs typically bind eukaryotic initiation factor 4G (eIF4G), a component of the eIF4F complex.
• The mechanism by which Hepatitis A virus (HAV) IRES translation requires eIF4E remained unexplained.

Purpose of the Study:

• To elucidate the regulatory mechanisms of HAV IRES-mediated translation by eIF4E.
• To investigate the role of eIF4E in poliovirus (PV) IRES translation and eIF4G processing.
• To understand the interplay between eIF4E, eIF4G, and viral IRES elements.

Main Methods:

• Biochemical assays to study protein-eIRES interactions.
• Analysis of translation rates in cell-free systems.
• Use of PV replicons and purified viral RNA.
• Investigation of eIF4G cleavage by the PV 2A protease.

Main Results:

• eIF4E binding to eIF4G enhances eIF4F complex affinity for the HAV IRES.
• eIF4E significantly stimulates the rate of RNA duplex unwinding by eIF4A on the IRES.
• eIF4E promotes eIF4F binding and restructuring of the PV IRES.
• eIF4E accelerates eIF4G cleavage by the PV 2A protease, generating a truncated eIF4G that stimulates eIF4A activity independently of eIF4E.

Conclusions:

• eIF4E employs dual mechanisms to regulate HAV IRES translation: enhancing eIF4F binding and stimulating RNA unwinding.
• eIF4E also promotes PV IRES restructuring and accelerates eIF4G cleavage.
• Cleavage of eIF4G by PV 2A protease generates a potent IRES-interacting fragment that bypasses the need for eIF4E in stimulating eIF4A activity.
• Picornavirus IRESs utilize both eIF4E-dependent and -independent pathways for translation regulation.