C to U editing of the anticodon of imported mitochondrial tRNA(Trp) allowsdecoding of the UGA stop codon in Leishmania tarentolae

All mitochondrial tRNAs in kinetoplastid protists are encoded in the nucleu s and imported into the organelle, The tRNA(Trp)(CCA) can decode the standa rd UGG tryptophan codon but can not decode the mitochondrial UGA tryptophan codon, We show that the mitochondrial tRNA(Trp) undergoes a specific C to U nucleotide modification in the first position of the anticodon, which all ows decoding of mitochondrial UGA codons as tryptophan. Functional evidence for the absence of a UGA suppressor tRNA in the cytosol, using a reporter gene, was also obtained, which is consistent with a mitochondrial localizat ion of this editing event. Leishmania cells have dealt with the problem of a lack of expression within the organelle of this non-universal tRNA by com partmentalizing an editing activity that modifies the anticodon of the impo rted tRNA.