Respiratory-deficient mutants of Torulopsis glabrata, a yeast with circular mitochondrial deoxyribonucleic acid of 6 mu m

Abstract

Purified mitochondria from the petite positive yeast T. glabrata contain a circular DNA with a length of 6 .mu.m and a buoyant density of 1.686 g/cm3. This DNA is absent from ethidium bromide-induced respiratory-deficient mutants. Additionally, a 2nd circular DNA component is present in both mutant and wild-type cultures with a length of 3 .mu.m and buoyant density of 1.710 g/cm3. Spontaneously arising respiratory-deficient mutants occur at a frequency of 10-5, which is 1,000-fold lower than in Saccharomyces cerevisiae. The mutants in T. glabrata each have mDNA lower in buoyant density than the wild type and this change is accompanied by the appearance of a large number of small circular molecules. In considering factors responsible for the decreased frequency of spontaneous mutants in T. glabrata, a suggestion is made that the mitochondrial genome in S. cerevisiae may be the result of 2 independent dimerizations of a basic 6-.mu.m molecule.