Translational Efficiency of a Non-AUG Initiation Codon Is Significantly Affected by Its Sequence Context in Yeast

Abstract Previous studies have shown that translation of mrna for yeast glycyl-tRNA synthetase is alternatively initiated from UUG and a downstream AUG initiation codon. Evidence presented here shows that unlike an AUG initiation codon, efficiency of this non-AUG initiation codon is significantly affected by its sequence context, in particular the nucleotides at positions –3 to –1 relative to the initiation codon. A/A/R (R represents A Or G) and C/G/C appear to be the most and least favorable sequences at these positions, respectively. Mutation of the native context sequence –3 to –1 from AAA to CGC reduced translation initiation from the UUG codon up to 32-fold and resulted in loss of mitochondrial respiration. although an AUG initiation codon is, in general, unresponsive to context changes in yeast, an AAA (–3 to –1) to CGC mutation still reduced its initiating activity up to 8-fold under similar conditions. these results suggest that sequence context is more important for translation initiation in yeast than previously appreciated.