title: Functional elements in initiation factors 1, 1A, and 2β discriminate against poor AUG context and non-AUG start codons.
abstract: Yeast eIF1 inhibits initiation at non-AUG triplets, but it was unknown whether it also discriminates against AUGs in suboptimal context. As in other eukaryotes, the yeast gene encoding eIF1 (SUI1) contains an AUG in poor context, which could underlie translational autoregulation. Previously, eIF1 mutations were identified that increase initiation at UUG codons (Sui(-) phenotype), and we obtained mutations with the opposite phenotype of suppressing UUG initiation (Ssu(-) phenotype). Remarkably, Sui(-) mutations in eukaryotic translation initiation factor 1 (eIF1), eIF1A, and eIF2β all increase SUI1 expression in a manner diminished by introducing the optimal context at the SUI1 AUG, whereas Ssu(-) mutations in eIF1 and eIF1A decrease SUI1 expression with the native, but not optimal, context present. Therefore, discrimination against weak context depends on specific residues in eIFs 1, 1A, and 2β that also impede selection of non-AUGs, suggesting that context nucleotides and AUG act coordinately to stabilize the preinitiation complex. Although eIF1 autoregulates by discriminating against poor context in yeast and mammals, this mechanism does not prevent eIF1 overproduction in yeast, accounting for the hyperaccuracy phenotype afforded by SUI1 overexpression.
authors.affiliation: Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Pilar
authors.initials: P
authors.lastname: Martin-Marcos
authors.forename: Yuen-Nei
authors.initials: YN
authors.lastname: Cheung
authors.forename: Alan G
authors.initials: AG
authors.lastname: Hinnebusch
mesh_terms: D019943:Amino Acid Substitution; D001483:Base Sequence; D018387:Codon, Initiator; D015977:Eukaryotic Initiation Factor-1 / Q000235:genetics / Q000378:metabolism*; D020717:Eukaryotic Initiation Factor-2B / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D015966:Gene Expression Regulation, Fungal; D017930:Genes, Reporter; D010442:Peptide Chain Initiation, Translational; D010641:Phenotype; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics
chemical_list: D018387:Codon, Initiator; D015977:Eukaryotic Initiation Factor-1; D020717:Eukaryotic Initiation Factor-2B; C072076:SUI1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C026022:eukaryotic peptide initiation factor-1A; D001616:beta-Galactosidase