Faculté des sciences

Dual targeting of a single tRNATrp requires two different tryptophanyl-tRNA synthetases in Trypanosoma brucei

Charrière, Fabien ; Helgadóttir, Sunna ; Horn, Elke K. ; Söll, Dieter ; Schneider, André

In: Proceedings of the National Academy of Sciences of the United States of America, 2006, vol. 103, p. 6847-6852

The mitochondrion of Trypanosoma brucei does not encode any tRNAs. This deficiency is compensated for by the import of a small fraction of nearly all of its cytosolic tRNAs. Most trypanosomal aminoacyl-tRNA synthetases are encoded by single-copy genes, suggesting the use of the same enzyme in the cytosol and mitochondrion. However, the T. brucei genome contains two distinct genes... More

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    Summary
    The mitochondrion of Trypanosoma brucei does not encode any tRNAs. This deficiency is compensated for by the import of a small fraction of nearly all of its cytosolic tRNAs. Most trypanosomal aminoacyl-tRNA synthetases are encoded by single-copy genes, suggesting the use of the same enzyme in the cytosol and mitochondrion. However, the T. brucei genome contains two distinct genes for eukaryotic tryptophanyl-tRNA synthetase (TrpRS). RNA interference analysis established that both TrpRS1 and TrpRS2 are essential for growth and required for cytosolic and mitochondrial tryptophanyl-tRNA formation, respectively. Decoding the mitochondrial tryptophan codon UGA requires mitochondria-specific C→U RNA editing in the anticodon of the imported tRNATrp. In vitro charging assays with recombinant TrpRS enzymes demonstrated that the edited anticodon and the mitochondria-specific thiolation of U33 in the imported tRNATrp act as antideterminants for the cytosolic TrpRS1. The existence of two TrpRS enzymes, therefore, can be explained by the need for a mitochondrial synthetase with extended substrate specificity to achieve aminoacylation of the imported thiolated and edited tRNATrp. Thus, the notion that, in an organism, all nuclear-encoded tRNAs assigned to a given amino acid are charged by a single aminoacyl-tRNA synthetase, is not universally valid.