[Genetic analysis of mitochondrial rho-mutability in Saccharomyces. I. Polygenic determination of spontaneous rho-mutability: gene-modifiers and srm mutation].

The phenotypic trait "starry colony" in Saccharomyces is associated with a high spontaneous rho- petite mutability. Genetic analysis of this trait has shown the high rho- mutability to be caused by several modifying genes present together in the cell genome. Every single modifying gene only produces a relatively small enhancement in the rho- mutability. Mutations in four nuclear srm (spontaneous rho- mutability) loci were isolated after mutagenic treatment of highly rho- mutable haploid cells. In contrast to the modifying genes, each of these mutations has a pronounced effect on the spontaneous rho- mutability, causing significant decrease in it.