CYTOPLASMIC TYROSYL-TRANSFER-RNA SYNTHETASE RESCUES THE DETECT IN MITOCHONDRIAL GENOME MAINTENANCE CAUSED BY THE NUCLEAR MUTATION MGM104-1 IN THE YEAST SACCHAROMYCES-CEREVISIAE

The yeast nuclear mutation mgm104-1, which leads to slow growth on glu cose medium and temperature-sensitive (ts) loss of mitochondrial DNA ( mtDNA), has been identified by screening a collection of temperature-s ensitive mutants on glycerol medium. A nuclear gene was isolated from a genomic DNA library by complementation of the mgm104-1 allele and wa s found to be identical to TTS1, which encodes the cytoplasmic tyrosyl -tRNA synthetase required for cytoplasmic protein synthesis. A gene di sruption in a diploid strain demonstrated that the TTS1 gene is essent ial for cell viability. The lack of mutations in TTS1 in the mgm104-1 mutant indicates that TTS1 and MGM104 are different genes. The ability to rescue the mgm104-1 phenotype with a single additional copy of TTS 1 suggests that TTS1 has an additional function that is directly or in directly involved in the maintenance of the mitochondrial genome.