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eIF2 independently binds two distinct eIF2B subcomplexes that catalyze and regulate guanine-nucleotide exchange
G D Pavitt1, K V Ramaiah, S R Kimball
1Laboratory of Eukaryotic Gene Regulation, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
Genes & Development
|March 21, 1998
Summary
Researchers identified how yeast translation initiation factor eIF2B is regulated by phosphorylated eIF2. Mutations in regulatory subunits GCN3 or GCD7 prevent inhibition, maintaining protein synthesis during stress.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- Eukaryotic protein synthesis initiation relies on the guanine-nucleotide exchange factor eIF2B.
- Stress conditions trigger eIF2B inhibition via phosphorylation of its substrate, eIF2, halting translation and cell growth.
Purpose of the Study:
- To investigate the mechanism of eIF2B inhibition by phosphorylated eIF2 [eIF2(alphaP)].
- To identify and characterize mutations in eIF2B that confer resistance to eIF2 phosphorylation-mediated inhibition.
Main Methods:
- In vitro nucleotide-exchange assays were used to measure eIF2B activity.
- Affinity-binding assays were employed to determine subunit interactions and binding affinities.
Main Results:
- Wild-type eIF2B is inhibited by eIF2(alphaP), while mutants in GCN3 or GCD7 remain active.
- A regulatory subcomplex (GCN3, GCD7, GCD2) binds eIF2(alphaP) with high affinity but lacks catalytic activity.
- A catalytic subcomplex (GCD1, GCD6) exhibits high nucleotide-exchange activity, independent of eIF2(alphaP).
Conclusions:
- eIF2B functions through distinct regulatory and catalytic subcomplexes.
- Phosphorylated eIF2 binding to the regulatory subcomplex inhibits nucleotide exchange by preventing interaction with the catalytic subcomplex.