title: Assembly of the mitochondrial membrane system. XIX. Genetic characterization of mit- mutants with deficiencies in cytochrome oxidase and coenzyme qh2-cytochrome c reductase.
abstract: Nineteen mutants of S. cerevisiae exhibiting a double deficiency in cytochrome oxidase and coenzyme QH2-cytochrome c reductase (also cytochrome b deficient) have been studied. The mutants have been crossed to a set of rho- tester strains with different segments of mitochondrial DNA. The mutants have also been crossed to mit- testers with defined genetic lesions. In addition, crosses were performed with a respiratory competent strain to ascertain whether mitotic and meiotic segregants could be isolated with only one of the two enzymatic deficiencies. The rho- testers allowed the doubly deficient mutants to be separated into two classes. Mutants in class 1 were not restored by any of the rho- testers and appeared to have separate mutations, one in cytochrome oxidase and the other in cytochrome b. Mutants in class 2 were restored by a set of rho- clones whose retained segments of mitochondrial DNA contained the cytochrome b but not the cytochrome oxidase loci. These appeared to behave as single hit mutations. Further studies, however, indicated that both class 1 and class 2 mutants carried separate mutations in two different loci. Mitotic and meiotic segregants with a single enzymatic deficiency could be isolated. In a number of strains, the mutations were mapped in known cytochrome oxidase and cytochrome b loci. The apparent discrepancy of the rho- tests for the class 2 mutants was shown to be probably due to a high unstability in one of the mutations. It has been concluded that all the doubly deficient strains carry two mutations in previously described cytochrome oxidase and cytochrome b loci. This conclusion argues against the existence of a single gene on mitochondrial DNA that controls the biosynthesis of the two respiratory enzymes.
mesh_terms: D002455:Cell Division; D003579:Cytochrome Reductases / Q000096:biosynthesis*; D004272:DNA, Mitochondrial; D003576:Electron Transport Complex IV / Q000096:biosynthesis*; D005796:Genes; D005816:Genetic Complementation Test; D008040:Genetic Linkage; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D014451:Ubiquinone / Q000096:biosynthesis*
chemical_list: D004272:DNA, Mitochondrial; D014451:Ubiquinone; D003579:Cytochrome Reductases; D003576:Electron Transport Complex IV