Translational efficiency of a non-AUG initiation codon is significantly affected by its sequence context in yeast.

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.

Cross-species and cross-compartmental aminoacylation of isoaccepting tRNAs by a class II tRNA synthetase.

It was previously shown that ALA1, the only alanyl-tRNA synthetase gene in Saccharomyces cerevisiae, codes for two functionally exclusive protein isoforms through alternative initiation at two consecutive ACG codons and an in-frame downstream AUG. We reported here the cloning and characterization of a homologous gene from Candida albicans. Functional assays show that this gene can substitute for both the cytoplasmic and mitochondrial functions of ALA1 in S.

An unusual pattern of protein expression and localization of yeast alanyl-tRNA synthetase isoforms.

Previous studies have shown that in Saccharomyces cerevisiae the mitochondrial and cytoplasmic forms of alanyl-tRNA synthetase are encoded by a single nuclear gene, ALA1, through alternative use of in-frame successive ACG triplets and a downstream AUG triplet. Here we show that despite the obvious participation of the non-AUG-initiated leader peptide in mitochondrial localization, the leader peptide per se cannot target a cytoplasmic passenger protein into mitochondria under normal conditions. Functional mapping further shows that an efficient targeting signal is composed of the leader peptide and an 18-residue sequence downstream of Met1.

Translation of a yeast mitochondrial tRNA synthetase initiated at redundant non-AUG codons.

Although initiation of translation at non-AUG codons occurs occasionally in prokaryotes and higher eukaryotes, it has not been reported in yeast until very recently. Evidence presented here shows that redundant ACG codons are recognized as alternative translation start sites for ALA1, the only gene in Saccharomyces cerevisiae coding for alanyl-tRNA synthetase. ALA1 is shown to be a bifunctional gene that provides both cytoplasmic and mitochondrial activities.