Cooperative modulation by eIF4G of eIF4E-binding to the mRNA 5' cap in yeast involves a site partially shared by p20

Area of Science:

• Molecular Biology
• Protein-Protein Interactions
• Eukaryotic Translation

Background:

• The interaction between the mRNA 5'-cap-binding protein eIF4E and the multiadaptor protein eIF4G is fundamental for eukaryotic translation initiation.
• Understanding this interaction is key to deciphering the regulation of protein synthesis.

Purpose of the Study:

• To map the specific surface amino acids on eIF4E involved in binding to eIF4G.
• To investigate the functional consequences of disrupting the eIF4E-eIF4G interaction on translation and cell growth.
• To compare the binding characteristics of eIF4G and the yeast 4E-binding protein p20 to eIF4E.

Main Methods:

• Immunological, genetic, and biochemical techniques were employed.
• Cap-analogue chromatography and surface plasmon resonance (SPR) were used to analyze binding affinities and kinetics.
• Mutagenesis studies were performed to identify critical residues on eIF4E.

Main Results:

• Specific surface regions and residues on eIF4E were identified as critical for eIF4G binding.
• Mutations in these regions disrupted eIF4E-eIF4G association, leading to impaired polysome formation, reduced growth, and temperature-sensitive defects in translation.
• The yeast protein p20 exhibits lower binding affinity to eIF4E than eIF4G and shares only a partial binding site, suggesting distinct regulatory roles.

Conclusions:

• The identified eIF4E residues are essential for positive cooperativity in eIF4G binding and cap affinity, directly impacting translation efficiency.
• The differential binding affinities and sites for eIF4G and p20 highlight their distinct roles in regulating protein synthesis, with p20 acting as a fine-tuner.
• This research provides a molecular basis for understanding the dynamic cycling of eIF4E and eIF4G in yeast translation.