The ?-hairpin of 40S exit channel protein Rps5/uS7 promotes efficient and accurate translation initiation in vivo.

ABSTRACT: The eukaryotic 43S pre-initiation complex bearing tRNAi(Met) scans the mRNA leader for an AUG start codon in favorable context. Structural analyses revealed that the ?-hairpin of 40S protein Rps5/uS7 protrudes into the 40S mRNA exit-channel, contacting the eIF2?GTP?Met-tRNAi ternary complex (TC) and mRNA context nucleotides; but its importance in AUG selection was unknown. We identified substitutions in ?-strand-1 and C-terminal residues of yeast Rps5 that reduced bulk initiation, conferred 'leaky-scanning' of AUGs; and lowered initiation fidelity by exacerbating the effect of poor context of the eIF1 AUG codon to reduce eIF1 abundance. Consistently, the ?-strand-1 substitution greatly destabilized the 'PIN' conformation of TC binding to reconstituted 43S·mRNA complexes in vitro. Other substitutions in ?-hairpin loop residues increased initiation fidelity and destabilized PIN at UUG, but not AUG start codons. We conclude that the Rps5 ?-hairpin is as crucial as soluble initiation factors for efficient and accurate start codon recognition.

SUBMITTER: Visweswaraiah J 

PROVIDER: S-EPMC4513230 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature