The three mutator strains anar-8, anar-14, and diur-301 were shown to produce respiratory deficient mutants at different rates. The frequency of respiratory deficient mutants in a culture could be increased by adding ethidium bromide. According to their cytochrome spectra and enzymatic activities they form three classes, namely mutants defective in cytochrome oxidase, in cytochrome b, and in both cytochromes. By restriction enzyme analysis of mitochondrial DNA from about 100 mutants, 22 deletion mutants were identified. The deletions, ranging from 50 to 1,500 base pairs were physically mapped. Deletions were localized in the genes coding for subunit 1 of cytochrome oxidase with its two introns, within the cytochrome b gene and its intron, and within the genes for subunits 2 and 3 of cytochrome oxidase. In several cases, where the physical mapping yielded ambiguous results, pairwise genetic crosses ruled out an overlap between two neighbouring deletions.
Using these mitochondrial deletion mutants as tester strains, it was shown that only tetrad analysis and chemical haploidization, but not mitotic segregation analysis, allows a decision between chromosomal and mitochon-Abbreviations. MtDNA = mitochondrial DNA; S. pombe = Schizosaccharomyces pombe; cox1, cox2, and cox3 refer to the mt genes coding for the three subunits of cytochrome oxidase; ATPase 6 (oli2), ATPase 8 (aapl in Saccharomyces cerevisiae, urf a61 in HeLa) and ATPase 9 (olil) refer to the three respective subunits of ATP synthase; cob is thegene for apocytochrome b; urf a is the single intergenic unassigned reading frame in S.
pornbe; 1 rRNA and s rRNA refer to the large and small ribosomal RNA, respectively. Mut-is a cytoplasmic mutator (the corresponding wild type allele is mut+). Mit-are mitochondrially inherited respiratory deficient mutants with mitochondrial protein synthesis; RC = respiratory competent, RD = respiratory deficient.
Offprint requests to. K. Wolf drial inheritance of respiratory deficiency in Schizosaccharomyces pombe.