title: Evidence that GCD6 and GCD7, translational regulators of GCN4, are subunits of the guanine nucleotide exchange factor for eIF-2 in Saccharomyces cerevisiae.
abstract: Starvation of the yeast Saccharomyces cerevisiae for an amino acid signals increased translation of GCN4, a transcriptional activator of amino acid biosynthetic genes. We have isolated and characterized the GCD6 and GCD7 genes and shown that their products are required to repress GCN4 translation under nonstarvation conditions. We find that both GCD6 and GCD7 show sequence similarities to components of a high-molecular-weight complex (the GCD complex) that appears to be the yeast equivalent of translation initiation factor 2B (eIF-2B), which catalyzes GDP-GTP exchange on eIF-2. Furthermore, we show that GCD6 is 30% identical to the largest subunit of eIF-2B isolated from rabbit reticulocytes. Deletion of either GCD6 or GCD7 is lethal, and nonlethal mutations in these genes increase GCN4 translation in the same fashion described for defects in known subunits of eIF-2 or the GCD complex; derepression of GCN4 is dependent on short open reading frames in the GCN4 mRNA leader and occurs independently of eIF-2 alpha phosphorylation by protein kinase GCN2, which is normally required to stimulate GCN4 translation. Together, our results provide evidence that GCD6 and GCD7 are subunits of eIF-2B in S. cerevisiae and further implicate this GDP-GTP exchange factor in gene-specific translational control.
authors.affiliation: Section on Molecular Genetics of Lower Eukaryotes, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
authors.forename: J L
authors.initials: JL
authors.lastname: Bushman
authors.forename: A I
authors.initials: AI
authors.lastname: Asuru
authors.forename: R L
authors.initials: RL
authors.lastname: Matts
authors.forename: A G
authors.initials: AG
authors.lastname: Hinnebusch
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000096:biosynthesis; D000818:Animals; D001483:Base Sequence; D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D020717:Eukaryotic Initiation Factor-2B; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D020662:Guanine Nucleotide Exchange Factors; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009154:Mutation; D010448:Peptide Initiation Factors / Q000096:biosynthesis; D014176:Protein Biosynthesis; D011487:Protein Conformation; D011494:Protein Kinases / Q000096:biosynthesis / Q000378:metabolism; D011506:Proteins / Q000737:chemistry* / Q000235:genetics; D011817:Rabbits; D012097:Repressor Proteins / Q000235:genetics*; D012156:Reticulocytes / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D000596:Amino Acids; D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2; D020717:Eukaryotic Initiation Factor-2B; D005656:Fungal Proteins; C079878:GCD6 protein, S cerevisiae; C079879:GCD7 protein, S cerevisiae; D020662:Guanine Nucleotide Exchange Factors; D046911:Macromolecular Substances; D010448:Peptide Initiation Factors; D011506:Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases