title: A nuclear mutation reversing a biased transmission of yeast mitochondrial DNA.
abstract: The highly biased transmission of p- mitochondrial DNA that occurs in hypersuppressive matings between p- and p+ cells of the yeast Saccharomyces cerevisiae is thought to be a consequence of the replication advantage of the p- mtDNA. A nuclear gene, MGT1, that is required for this displacement of p+ mtDNA from zygotic clones has been identified through mutation. When one haploid parent carries the mgt1 allele, transmission of p- mtDNA is substantially reduced. When both haploid parents carry the mgt1 allele, p- mtDNA is essentially eliminated from the zygotic progeny. Thus in the absence of the MGT1 gene there is a switch in the transmission bias; p+ mtDNA rather than the hypersuppressive p- mtDNA is inherited by most zygotic clones. In contrast to its semi-dominant behavior in haploid matings, mgt1 behaves as a recessive allele in diploid matings since the p+ genome in MGT1/mgt1 diploids is efficiently displaced when mated with a MGT1/mgt1 hypersuppressive p- diploid strain. We find that p+ genomes can be comaintained along with hypersuppressive p- mtDNA for extended periods in clonal lines derived from MGT1 x mgt1 matings. However, as expected from the recessive nature of the mgt1 mutation, these p+ genomes are eventually eliminated. Our work indicates that MGT1 plays a crucial role in the competition for inheritance between hypersuppressive p- mtDNAs and the p+ mitochondrial genome. The MGT1 gene product may be a component of a mtDNA replication system that acts preferentially at the rep sequences found in hypersuppressive mtDNAs.
authors.affiliation: Department of Genetics, University of Washington, Seattle 98195.
authors.forename: S G
authors.initials: SG
authors.lastname: Zweifel
authors.forename: W L
authors.initials: WL
authors.lastname: Fangman
mesh_terms: D002467:Cell Nucleus; D015825:Chromosomes, Fungal; D003433:Crosses, Genetic; D004261:DNA Replication; D004271:DNA, Fungal / Q000096:biosynthesis / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000096:biosynthesis / Q000235:genetics*; D015870:Gene Expression; D005800:Genes, Fungal; D005808:Genes, Recessive; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000235:genetics*
chemical_list: D004271:DNA, Fungal; D004272:DNA, Mitochondrial