The mitochondrial genome of wild-type yeast cells: VIII. The spontaneous cytoplasmic “petite” mutation☆

Abstract The mitochondrial genomes of a number of spontaneous “petite” mutants of Saccharomyces cerevisiae were investigated by restriction enzyme analysis and by hybridization with restriction fragments from parental wild-type genomes. The nucleotide sequences forming the ends of the repeat units of the petite genomes were shown to be formed by GC clusters and, possibly, by AT spacers. These non-coding elements are characterized by the fact that they consist of, or contain, sequences which are repeated a number of times in the parental, wild-type genome and which are often symmetrical. The excision process leading to the formation of the spontaneous petite genomes appears to involve site-specific, illegitimate recombination events which take advantage of localized sequence homology, in agreement with a deletion model previously proposed. The same kind of excision process appears to be operative in the further deletions undergone by the mitochondrial genomes of spontaneous petite mutants. The genome organization and the excision mechanism appear to be largely different in spontaneous and ethidium-induced petite mutants.