Translation initiation factor 2gamma mutant alters start codon selection independent of Met-tRNA binding.
Selection of the AUG start codon for translation in eukaryotes is governed by codon-anticodon interactions between the initiator Met-tRNA(i)(Met) and the mRNA. Translation initiation factor 2 (eIF2) binds Met-tRNA(i)(Met) to the 40S ribosomal subunit, and previous studies identified Sui(-) mutations in eIF2 that enhanced initiation from a noncanonical UUG codon, presumably by impairing Met-tRNA(i)(Met) binding. Consistently, an eIF2gamma-N135D GTP-binding domain mutation impairs Met-tRNA(i)(Met) binding and causes a Sui(-) phenotype. Intragenic A208V and A382V suppressor mutations restore Met-tRNA(i)(Met) binding affinity and cell growth; however, only A208V suppresses the Sui(-) phenotype associated with the eIF2gamma-N135D mutation. An eIF2gamma-A219T mutation impairs Met-tRNA(i)(Met) binding but unexpectedly enhances the fidelity of initiation, suppressing the Sui(-) phenotype associated with the eIF2gamma-N135D,A382V mutant. Overexpression of eIF1, which is thought to monitor codon-anticodon interactions during translation initiation, likewise suppresses the Sui(-) phenotype of the eIF2gamma mutants. We propose that structural alterations in eIF2gamma subtly alter the conformation of Met-tRNA(i)(Met) on the 40S subunit and thereby affect the fidelity of start codon recognition independent of Met-tRNA(i)(Met) binding affinity.
Alone
Pankaj V
PV
Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Cao
Chune
C
Dever
Thomas E
TE
D000595:Amino Acid Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D018387:Codon, Initiator / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D010641:Phenotype; D017434:Protein Structure, Tertiary; D012358:RNA, Transfer, Met / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D050976:Basic-Leucine Zipper Transcription Factors; D018387:Codon, Initiator; D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2; C501391:GCN4 protein, S cerevisiae; D012358:RNA, Transfer, Met; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors
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