Dual targeting of a single tRNA(Trp) requires two different tryptophanyl-tRNA synthetases in Trypanosoma brucei.
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 tRNA(Trp). In vitro charging assays with recombinant TrpRS enzymes demonstrated that the edited anticodon and the mitochondria-specific thiolation of U33 in the imported tRNA(Trp) 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 tRNA(Trp). 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.
Charrière
Fabien
F
Department of Biology/Cell and Developmental Biology, University of Fribourg, Chemin du Musée 10, CH-1700 Fribourg, Switzerland.
Helgadóttir
Sunna
S
Horn
Elke K
EK
Söll
Dieter
D
Schneider
André
A
D000595:Amino Acid Sequence; D000818:Animals; D007527:Isoenzymes / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D030781:Organisms, Genetically Modified; D010802:Phylogeny; D034622:RNA Interference; D012364:RNA, Transfer, Trp / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D014369:Tryptophan-tRNA Ligase / Q000145:classification / Q000235:genetics / Q000378:metabolism*
D007527:Isoenzymes; D012364:RNA, Transfer, Trp; D014369:Tryptophan-tRNA Ligase