The bivious suppressiveness of cytoplasmic petites of S. cerevisiae lacking in mitochondrial DNA

Determinant for multiple drug resistance possessing features of a mitochondrial episome in Saccharomyces cerevisiae

A mutation for multiple resistance to tetracycline, cycloheximide and oligomycin appears to be followed by reconstruction of the mitochondrial genome resulting in the formation of independent nucleotide sequences that determine different resistant phenotypes. Heterozygotes for the cross resistance factor lack locus T responsible for relation tetracycline which comes from the alpha-parent. The nuclear recessive gene-suppresor i induces deletion of the whole determinant for multiple resistance. The loss of mt-DNA on ethidium bromide treatment does not lead to the loss of this determinant which remains in the cells either in an active or in a passive state.

Pattern of somatic segregation of the cytoplasmic drug-resistance factors in yeast

The pattern of somatic segregation of the cytoplasmic factors confering resistances to chloramphenicol, erythromycin and oligomyin in S. cerevisiae was studied. The fractions of the zygotes heterozygous for the chloramphenicol-resistance factor and for the erythromycin-resistance factor decreased exponentially with generation number of zygotes. The rate of the segregation was highest for the chloramphenicol-resistance factor and lowest for the oligomycin-resistance factor. The segregation rate as well as the transmission polarity of the chloramphenicol-resistance factor varied with different carbon sources with which the parental haploids were grown prior to mating.

The segregation of mitochondrial genes in yeast. I. Analysis of zygote pedigrees of petite X grande crosses

A large number of spontaneous, cytoplasmic petite mutants from six grande strains of Saccharomyces cerevisiae were crossed to a pair of isogenic tester strains. Suppressivity values were obtained by randomly sampling the diploid progeny from these crosses, and this basis, crosses were broadly categorized as having high, intermediate, or low suppressivity. For each cross, individual zygotes were obtained also. All successive first-generation buds were isolated from the zygotes, and analyzed for the presence of petite genotypes. We found that, though early buds may be mixed, all zygotes eventually produce a succession of buds which have the same genotype--either all petite or all grande. Many more zygotes from crosses in all categories of suppressivity purified to petite than expected from the population values for suppressivity. Reconstruction experiments indicate that most petite mutants may actually generate over 90% petite progeny in a petite X grande cross.

Genetic analysis of unequal transmission of the mitochondrial markers in Saccharomyces cerevisiae

The presence of mitochondrial sex factor, omega, was demonstrated in haploid strains of yeast Saccharomyces cerevisiae which came from our laboratory. Transmission and recombination of the mitochondrial genes (CR/CS, ER/ES and OR/OS), conferring the resistance/sensitivity to chloramphenicol, erythromycin and oligomycin, respectively, were non-polar in homosexual crosses and highly polar in heterosexual crosses. Different results were obtained in crosses involving an erythromycin resistant mutant G706E11 (CSEROS) which was found to contain cellular DNA of diploid level. This strain was omega- and showed no alleles from G706E11 (CS, ER and OS) were transmitted to the zygote progeny in preference to the CR, ES and OR alleles. When crossed to omega+ haploid strains, there was a highly polar recombination, but no transmission was seen for the E and O alleles. Polar transmission of markers from omega+ haploid parental strain, characteristic of heterosexual crosses, was noticed only for the C allele. The crosses of G706E11 to omega+ haploids featured an increase in the recombination frequency. The values of % suppressiveness of sigma- petite mutants were relatively low when determined by crossing to G706E11 or to sigma+ diploid strain M2-8C rather than by crossing to sigma+ haploid strains, indicating that there is a positive correlation between the polar transmission of drug resistance markers and the suppressiveness degrees. Genetic mechanism of the anomalous behaviors if mitochondrial genes in crosses involving G706E11 was discussed and interpreted as due to an unbalanced supply of mitochondrial genomes from parental strains.

Cytoplasmically inherited ethidium bromide resistance in suppressive petites of Saccharomyces cerevisiae

Neutral petites were induced in three different [rho+] strains by treating with ethidium bromide. However, EB treatment of spontaneously generated suppressive petites, which were derived from the same [rho+] strains, produced no neutral petites and moreover had little or no effect on the suppressiveness of the petities. Genetic analysis showed that the ethidium bromide resistance of the suppressive petites was a manifestation of cytoplasmically inherited, respiratory deficiency.