Preferential delection of a specific region of mitochondrial DNA in Saccharomyces cerevisiae by ethidium bromide and 3-carbethoxy-psoralen

Abstract

Grande strains of Saccharomyces cerevisiae were mutagenized either by ethidium bromide or by 3-carbethoxy-psoralen (a monofunctional furocoumarin derivative) activated by 365 nm light. 973 primary rho⁻ clones induced were randomly collected and analyzed individually for the presence or absence of fifteen mitochondrial genetic markers. Under mild conditions of mutagenesis, 83% of the primary clones showed single-deletion genotypes; a unique order of 14 markers could be deduced from the patterns of the deletion. The gene order confirmed our previous map constructed from the analysis of established non-random petite clones. From the frequencies of disjunction between markers, the distances separating 14 mitochondrial markers were estimated. One region, carrying oxi-3, pho-1 and mit 175 loci, was preferentially lost in rho⁻ mutants: there is a strong constraint in the frequencies of various genotypes found in rho⁻ clones. On each side of this particular region, a bidirectionally oriented pattern of retention of markers is observed.