ASSEMBLY OF THE MITOCHONDRIAL MEMBRANE SYSTEM: NUCLEAR SUPPRESSION OF A CYTOCHROME b MUTATION IN YEAST MITOCHONDRIAL DNA

Gloria Coruzzi ¹ and Alexander Tzagoloff ¹

¹ Department of Biological Sciences, Columbia University, New York, N. Y. 10027

In a previous study, a mitochondrial mutant expressing a specific enzymatic deficiency in co-enzyme QH₂-cytochrome c reductase was described (Tzagoloff, Foury and Akai 1976). Analysis of the mitochondrially translated proteins revealed the absence in the mutant of the mitochondrial product corresponding to cytochrome b and the presence of a new low molecular weight product. The premature chain-termination mutant was used to obtain suppressor mutants with wild-type properties. One such revertant strain was analyzed genetically and biochemically. The revertant was determined to have a second mutation in a nuclear gene that is capable of partially suppressing the original mitochondrial cytochrome b mutation. Genetic data indicate that the nuclear mutation is recessive and is probably in a gene coding for a protein involved in the mitochondrial translation machinery.