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Proc Natl Acad Sci U S A. 1993 Jun 1;90(11):5350-4.

A protein complex of translational regulators of GCN4 mRNA is the guanine nucleotide-exchange factor for translation initiation factor 2 in yeast.

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  • 1Section on Molecular Genetics of Lower Eukaryotes, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.


In Saccharomyces cerevisiae, phosphorylation of the alpha subunit of translation initiation factor 2 (eIF-2) by protein kinase GCN2 stimulates translation of GCN4 mRNA. In mammalian cells, phosphorylation of eIF-2 alpha inhibits the activity of eIF-2B, the GDP-GTP exchange factor for eIF-2. We present biochemical evidence that five translational regulators of GCN4 encoded by GCD1, GCD2, GCD6, GCD7, and GCN3 are components of a protein complex that stably interacts with eIF-2 and represents the yeast equivalent of eIF-2B. In vitro, this complex catalyzes guanine nucleotide exchange on eIF-2 and overcomes the inhibitory effect of GDP on formation of eIF-2.GTP.Met-initiator tRNA(Met) ternary complexes. This finding suggests that mutations in GCD-encoded subunits of the complex derepress GCN4 translation because they mimic eIF-2 alpha phosphorylation in decreasing eIF-2B activity. Our results indicate that translational control of GCN4 involves a reduction in eIF-2B function, a mechanism used in mammalian cells to regulate total protein synthesis in response to stress.

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