Reintroduction of a characterized mit tRNAgly mutation into yeast mitochondria provides a new tool for the study of human neurodegenerative diseases

We report the identi®cation and characterization of a new mutation (ts9) in the Saccharomyces cerevisiae mitochondrial genome, which was ®rst genetically mapped in the tRNAgly region and further identi®ed by means of sequencing as consisting of a G to A transition at position 30 in the tRNA. The mutation causes an almost complete disappearance of mature tRNAgly, while a second mitochondrial mutation with a compensatory C to T change restores it in normal quantities; this points to the importance of the strong bond between bases 30 and 40 of the anticodon stem in the stabilization of the tRNA. In addition to resulting in a clear-cut heat-sensitive phenotype, the ts9 mutation creates a new EcoRV restriction site. Both properties were used as markers to monitor the successful (re) introduction of the mutated allele into a wild-type mitochondrial genome through biolistic transformation. The mutant frequency in the progeny as well as the correct integration of the mutated allele at its proper site demonstrate the feasibility of this method for creating and investigating speci®c mitochondrial tRNA mutations. The method will provide important applications for the use of yeast as a model system of human mitochondrial pathologies.