Determination of the degree of suppressivity of Saccharomyces cerevisiae strain RD I A

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

Mutants, called p-, 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 p- cells, often as head-to-tail multimers, producing a cell with the normal amount of mitochondrial DNA. In matings, some of these p- mutants exhibit zygotic hypersuppressiveness, excluding the wild-type mitochondrial genome (p+) from all the diploids that are produced. From a hypersuppressive p- strain, we isolated two mutants with reduced suppressiveness. These mutants, one moderately suppressive and one nonsuppressive, retain only 89 and 70 base pairs, respectively, of the wild-type mitochondrial genome. Their sequences consist of 100% A . 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 . C base pair.

Cytoplasmic inheritance in Saccharomyces cerevisiae: comparison of first zygotic budsite to mitochondrial inheritance patterns

Zygotic first budsite in Saccharomyces cerevisiae was studied in relation to defined mitochondrial inheritance systems: both petite and drug resistance. It was hypothesized that a highly asymmetric inheritance pattern would be correlated to a high frequency of first budsites on the petite or drug resistant end of the zygote (i.e., that portion of the zygote which was originally the drug resistant or petite haploid before zygote formation). The data collected did not support the hypothesis. For drug resistance, the budsite pattern is identical for a highly biased and a moderately biased inheritance pattern. In a grande by grande cross there is a high probability of the first bud appearing on the conjugation bridge, with lower but equal probabilities of the first bud appearing on one end or the other of the zygote. A grande by petite cross changes this pattern to a high probability of the first bud appearing on the grade end of the zygote, with a lesser probability of the first bud appearing on the conjugation bridge and virtually no budding of the petite end. This phenomenon is independent of degree of neutrality or suppressiveness of the petite strain used, however. The difference between a grande and a grande by petite pattern may be due to the relative functional ability of the mitochondria in each end of the zygote. Tests using antimitochondrial drugs suggest that selection of first budsite on a zygote is a complex phenomenon, not simply dependent upon mitochondrial phenotype. In conclusion, selection of the first zygotic budsite appears to be independent of mitochondrial inheritance patterns.

Manganese mutagenesis in yeast. II. Conditions of induction and characteristics of mitochondrial respiratory deficient Saccharomyces cerevisiae mutants induced with manganese and cobalt

Manganese and cobalt are capable of inducing ρ−mutations* in non-growing cells ofSaccharomyces cerevisiae, but their mutagenic action is much stronger in growing cells. At a given concentration cobalt and manganese can be either strongly mutagenic or non-mutagenic, depending on the cell density.

Most of the ρ−mutants induced with manganese and a considerable proportion of those induced with cobalt are suppressive and/or transmit drug resistance markers, so they must still carry mitochondrial DNA. Cobalt can decrease suppressiveness with low efficiency and eliminate drug resistance markers from established ρ−clones.