A genetic link between an mRNA-specific translational activator and the translation system in yeast mitochondria

Translation of the Saccharomyces cerevisiae mitochondrial mRNA encoding cytochrome c oxidase subunit III (coxIII) specifically requires the products of at least three nuclear genes, PET122, PET494 and PET54 . pet122 mutations that remove 24-67 amino acid residues from the carboxyterminus of the gene product were found to be suppressed by unlinked nuclear mutations. One of the suppressor mutations causes a heat-sensitive nonrespiratory growth phenotype in an otherwise wild-type strain and reduces translation of all mitochondrial gene products in cells grown at high temperature. This suppressor maps to a newly identified gene on chromosome XV termed PET123 . The sequence of a DNA fragment carrying PET123 contains one major open reading frame encoding a basic protein of 318 amino acids. Inactivation of the chromosomal copy of PET123 by interruption of this open reading frame causes cells to become rho super(-) (sustain large deletions in their mtDNA).