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Translation initiation factor 3 antagonizes authentic start codon selection on leaderless mRNAs
Author(s) -
Tedin Karsten,
Moll Isabella,
Grill Sonja,
Resch Armin,
Graschopf Anton,
Gualerzi Claudio O.,
Bläsi Udo
Publication year - 1999
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1999.01147.x
Subject(s) - biology , start codon , translation (biology) , eukaryotic translation , ribosome , initiation factor , ternary complex , translational regulation , messenger rna , ribosomal binding site , microbiology and biotechnology , genetics , gene , rna , biochemistry , enzyme
In this study, we have examined the influence of initiation factors on translation initiation of leaderless mRNAs whose 5′‐terminal residues are the A of the AUG initiating codon. A 1:1 ratio of initiation factors to ribosomes abolished ternary complex formation at the authentic start codon of different leaderless mRNAs. Supporting this observation, in vitro translation assays using limiting ribosome concentrations with competing leaderless λ c I and Escherichia coli ompA mRNAs, the latter containing a canonical ribosome binding site, revealed reduced cI synthesis relative to OmpA in the presence of added initiation factors. Using in vitro toeprinting and in vitro translation assays, we show that this effect can be attributed to IF3. Moreover, in vivo studies revealed that the translational efficiency of a leaderless reporter gene is decreased with increased IF3 levels. These studies are corroborated by the observed increased translational efficiency of a leaderless reporter construct in an infC mutant strain unable to discriminate against non‐standard start codons. These results suggest that, in the absence of a leader or a Shine–Dalgarno sequence, the function(s) of IF3 limits stable 30S ternary complex formation.