William E. Lancashire

Evidence for an extra-chromosomal element involved in mitochondrial function: A mitochondrial episome?

Biochemical genetic studies of cytoplasmic mutants of Saccharomyces cerevisiae resistant to inhibitors of aerobic (mitochondrial) metabolism such as oligomycin and venturicidin have shown that the resistance determinants are located on mitochondrial DNA [ 1,2]. Three separate loci, OL 1, OL II and OL III which probably specify two different subunits of the mitochondrial ATPase complex have been identified [2-41. Other mutants resistant to inhibitors and uncouplers with a specific mode of action on aerobic energy conservation reactions are under investigation including triethyltin, ‘1799’, bongkrekic acid, rhodamine 6G and valinomycin. Detailed studies of cytoplasmic triethyltin mutants and another class of venturicidin resistant mutants [2,5] indicate that these resistance determinants are unlinked to other loci on mt-DNA suggesting that the VENRTETR determinants are located on a cytoplasmic DNA species different from mt-DNA [2]. However, there are several features of these mutants which suggest a close association with mitochondrial function, e.g. the loss of the VENRTETR phenotype on ethidium bromide treatment always leads to the pstate and a significant proportion of spontaneous petites co-) have lost resistance determinants. In this paper we present evidence that the VENR TETR resistance determinants are located on a cytoplasmic DNA species other than mt-DNA. Our studies

Extra-chromosomal inheritance of rhodamine 6G resistance in Saccharomyces cerevisiae.

SummaryRhodamine 6G was found to be a specific inhibitor of aerobic growth of yeast, having no effect on fermentative growth. A single step spontaneous mutant of S. cerevisiae resistant to rhodamine 6G was isolated, which showed cross-resistance to the ATPase inhibitors venturicidin and triethyltin, to the uncoupler 1799, to bongkrekic acid and to cycloheximide, but not to oligomycin or to the inhibitors of mitochondrial protein synthesis, chloramphenicol and erythromycin. The genetic analysis of this mutant showed that both nuclear and cytoplasmic (but apparently not mitochondrial) factors may be involved in the determination of the mutation. The behaviour is discussed as a possible function for 2 micron circular (omicron) DNA.

Genetics of oxidative phosphorylation: Petite deletion mapping of the Oli 2 region of the mitochondrial genome of Saccharomyces cerevisiae

SummaryPetite deletion mapping has been carried out for the Oli 2 region of the mitochondrial genome of Saccharomyces cerevisiae to produce a fine structure genetic map. Previously unlocated mit- mutants together with the drug resistant loci Oli 2 and Oss 1 have been ordered between the cytochrome oxidase and apocytochrome b genes.As a result of this study a series of isogenic p- clones have been isolated spanning the Oli 2 region.

Genetics of oxidative phosphorylation: Allelism studies of mitochondrial loci in the PHO1—OLI2 region of the genome

SummaryIn a search for new aerobic-growth deficiency mutations affecting mitochondrial energy-conservation two mit− mutations, namely pho-8 and pho-9, have been isolated.The two mutations are allelic with each other, but not allelic with the previously known pho1 mutations although close linkage is indicated.Allelism studies define three distinct PHO loci clustered in this region which also includes the drugresistance loci OSS1, OLI2 and OLI4. The existence of phenotypically-distinct markers makes the region amenable to fine-structure mapping.