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An eIF5/eIF2 complex antagonizes guanine nucleotide exchange by eIF2B during translation initiation
Chingakham Ranjit Singh1, Bumjun Lee, Tsuyoshi Udagawa
1Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, 66506, USA.
The EMBO Journal
|September 23, 2006
Summary
The eIF2/eIF5 complex acts as a cytoplasmic reservoir for eIF2, regulating translation initiation by opposing eIF2B activity. This finding clarifies the physiological role of eIF2/eIF5 interactions in eukaryotic cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Eukaryotic translation initiation involves the ternary complex (TC) and multifactor complex (MFC).
- The guanine nucleotide exchange factor eIF2B is crucial for recycling eIF2.
- eIF5 and eIF2Bε share an eIF2-binding site, suggesting potential competition.
Purpose of the Study:
- Investigate the physiological significance of the eIF2/eIF5 complex lacking Met-tRNA(i)(Met).
- Determine how eIF5 and eIF2Bε interact with eIF2 and influence translation initiation.
- Clarify the role of Met-tRNA(i)(Met) in MFC assembly.
Main Methods:
- Overexpression of eIF5 and its mutants.
- Site-directed mutagenesis of eIF2B subunits, particularly eIF2Bε.
- Analysis of complex formation (eIF2/eIF5, TC/eIF5, MFC) and guanine nucleotide exchange.
Main Results:
- eIF5 overexpression increases eIF2/eIF5 and TC/eIF5 complexes, inhibiting eIF2B and MFC formation.
- eIF2Bε mutations enhance eIF5's ability to compete for eIF2, indicating eIF2Bε normally disrupts eIF2/eIF5 interaction.
- Overexpressed eIF2Bε competes with MFC, and eIF5 overexpression does not form aberrant MFC lacking tRNA(i)(Met).
Conclusions:
- The eIF2/eIF5 complex serves as a cytoplasmic reservoir for eIF2.
- This complex antagonizes eIF2B-mediated guanine nucleotide exchange, impacting translation initiation.
- Met-tRNA(i)(Met) is essential for proper MFC assembly.
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