Yeast mitochondrial genomes consisting of only A.T base pairs replicate and exhibit suppressiveness.

Abstract

Mutants, called .rho.-, that result from extensive deletions of the 75-kilobase Saccharomyces cerevisiae mitochondrial genome arise at high frequency. The remaining mitochondrial DNA is amplified in the .rho. cells, often as head-to-tail multimers, producing a cell with the normal amount of mitochondrial DNA. In matings, some of these .rho. mutants exhibit zygotic hypersuppressiveness, excluding the wild-type mitochondrial genome (.rho.+) from all the diploids that are produced. From a hypersuppressive .rho.- strain, 2 mutants with reduced suppressiveness were isolated. These mutants, one moderately suppressive and the other nonsuppressive, retain only 89 and 70 base pairs, respectively, of the wild-type mitochondrial genome. Their sequences consist of 100% A .cntdot. T base pairs. Replication of DNA in the mitochondrion, formation and amplification of new deletion genomes, and exhibition of suppressiveness do not require a single G .cntdot. C base pair.