Cytoplasmic and nuclear inheritance of resistance to alkylguanidines and ethidium bromide in a petite-negative yeast

Protoplast fusion in a petite-negative yeast, Kluyveromyces lactis

The technique of protoplast fusion has been applied to the problem of unstable diploidy in the yeast Kluyveromyces lactis. By protoplast fusion between heterothallic strains of like mating-type, sporulation-deficient hybrids can be obtained. Biochemical, cytological, and genetical characterisation of these hybrids suggests that the majority of fusion products are diploid. Sporulating hybrids can be constructed by protoplast fusion between homothallic strains. Tetrad analysis of these hybrids demonstrates conclusively the diploid nature of fusion products.

Nuclear and cytoplasmic cross-resistance and correlated sensitivity to DNA intercalating drugs in a petite-negative yeast

Ethidium bromide and acriflavin-resistant mutants of petite-negative yeast Kluyveromyces lactis were prepared. One kind of nuclear mutation (EBR1) gave resistance to ethidium bromide and correlated sensitivity towards acriflavin. Another nuclear mutation (EBR2) did not affect ‘natural’ resistance of this yeast towards 15 μM acriflavin. Both nuclear mutations mapped at different loci, suggesting lack of linkage. Cytoplasmic mutants resistant to these two drugs were unstable when grown in complete media with dextrose, reverting to a wild-type resistance genotype. When grown in glycerol-containing media these mutants maintained their cytoplasmic drug-resistance conferring factors.

NET1 and HFI1 genes of yeast mediate both chromosome maintenance and mitochondrial rho(-) mutagenesis

An increase in the mitochondrial rho(-) mutagenesis is a well-known response of yeast cells to mutations in numerous nuclear genes as well as to various kinds of stress. Despite extensive studies for several decades, the biological significance of this response is still not fully understood. The genetic approach to solving this enigma includes a study of genes that are required for the high incidence of spontaneous rho(-) mutants. We have obtained mutations of a few nuclear genes of that sort and found that mutations in certain genes, including CDC28, the central cell-cycle regulation gene, result in a decrease in spontaneous rho(-) mutability and simultaneously affect the maintenance of the yeast chromosomes and plasmids. Two more genes resembling CDC28 in this respect are identified in the present work as a result of the characterization of four new mutants. These two genes are NET1 and HFI1 which mediate important regulatory protein-protein interactions in the yeast cell. The effects of four mutations, including net1-srm and hfi1-srm, on the maintenance of the yeast mitochondrial genome, chromosomes and plasmids, as well as on the cell's sensitivity to ionizing radiation, are also described. The data presented suggest that the pleiotropic srm mutations determining coordinate changes in the fidelity of mitotic transmission of chromosomes, plasmids and mtDNA molecules identify genes that most probably operate high up in the hierarchy of the general genetic regulation of yeast.

Characterization of the histidine mutants of Kluyveromyces lactis

Thirty-eight different histidine mutations of Kluyveromyces lactis were isolated and genetically characterized. All of the mutations were nuclear recessive alleles. They turned out to belong to seven different complementation groups, designated hisA1 to hisA7. Five of these genes have been cloned by in vivo complementation of the Klhis mutations. Their homology to some of the histidine genes of Saccharomyces cerevisiae was confirmed by heterologous complementation. However, one of these KlHIS genes did not complement any mutation in the seven known histidine biosynthetic enzymes encoding genes (his1-his7) of S. cerevisiae.

The red ade mutants of Kluyveromyces lactis and their classification by complementation with cloned ADE1 or ADE2 genes from Saccharomyces cerevisiae

Seventy-six red adenine mutants of Kluyveromyces lactis were isolated. By complementation they could be assigned to two groups with 31 and 45 mutants. Transformation of several strains from each group with plasmids containing the Saccharomyces cerevisiae ADE1 or ADE2 gene showed that the largest group was ade2 and the other group was ade1. Several previously isolated 'ade1' mutants were classified to either group and given new gene and allele numbers. ADE1 was localized at chromosome III, closely linked to the mating type gene, making it a convenient marker for mating type. ADE2 was localized at chromosome V.

Molecular cloning of the plasma membrane H(+)-ATPase from Kluyveromyces lactis: a single nucleotide substitution in the gene confers ethidium bromide resistance and deficiency in K+ uptake

A Kluyveromyces lactis strain resistant to ethidium bromide and deficient in potassium uptake was isolated. Studies on the proton-pumping activity of the mutant strain showed that a decreased H(+)-ATPase specific activity was responsible for the observed phenotypes. The putative K. lactis PMA1 gene encoding the plasma membrane H(+)-ATPase was cloned by its ability to relieve the potassium transport defect of this mutant and by reversing its resistance to ethidium bromide. Its deduced amino acid sequence predicts a protein 899 residues long that is structurally colinear in its full length to H(+)-ATPases cloned from different yeasts, except for the presence of a variable N-terminal domain. By PCR-mediated amplification, we identified a transition from G to A that rendered the substitution of the fully conserved methionine at position 699 by isoleucine. We attribute to this amino acid change the low capacity of the mutant H(+)-ATPase to pump out protons.

Induction by glucose of an antimycin-insensitive, azide-sensitive respiration in the yeast Kluyveromyces lactis

Increasing the glucose concentration from 0.1 to 10% in exponentially growing cultures of Kluyveromyces lactis CBS 2359 does not repress the antimycin-sensitive respiration (QO2 of 80 microliter O2 . h-1 . mg-1 dry weight) but raises the antimycin-insensitive respiration from 3 to 12 microliter O2 . h-2 . mg-1 dry weight. Antimycin A inhibits the growth of K. lactis on a variety of substrates with the exception of glucose at concentrations equal to or higher than 1% where substantial antimycin-insensitive respiratory rates are induced. It can be concluded that a minimal antimycin-insensitive QO2 is necessary for cellular growth when the normal respiratory pathway is not functional. The antimycin-insensitive respiration elicited by growth in high glucose concentrations is poorly inhibited by hydroxamate and is inhibited by 50% by 90 microM azide or 1 mM cyanide. These concentrations are much higher than those necessary to inhibit cytochrome c oxidase which is not involved in the antimycin-insensitive respiration as was demonstrated by spectral measurements. A pigment absorbing at 555 nm is specifically reduced after addition of glucose to antimycin-inhibited cells. The same pigment is reoxidized by further addition of high concentrations of sodium azide indicating its participation in the antimycin-insensitive, azide-sensitive respiration.

Extrachromosomal inheritance in Schizosaccharomyces pombe. IV. Isolation and genetic characterization of mutants resistant to chloramphenicol and erythromycin using the mutator properties of mutant anar-8

Spontaneous chloramphenicol (capr)- and erythromycin (eryr)-resistant mutants were isolated from strain ade7-50 h- and the antimycin-resistant mutant anar-8 ade 7-50 h- of Schizosaccharomyces pombe (Sch. p.). By mitotic segregation analysis all 154 capr- and 120 eryr-mutants derived from ade 7-50 h- proved to be recessive chromosomal, whereas all 108 capr- and 200 eryr-mutants originating from anar-8 were extrachromosomally inherited. The rate of spontaneous capr- and eryr-mutants was about hundredfold in anar-8 compared to ade 7-50 h-. Growth of capr- and eryr-mutants was not inhibited by chloramphenicol or erythromycin, respectively, in glucose-medium and only slightly in glycerol-medium at concentrations which completely inhibited anar-8. By mitotic segregation-, tetrad-, and mitotic haploidization-analysis the extrachromosomal inheritance of mutants derived from anar-8 was established. Segregational patterns of capr- and eryr-determinants during mitosis, meiosis, and mitotic haploidization of diploids are discussed.

Chromosomal and extrachromosomal inheritance of erythromycin-resistance in the "petite-negative" yeast Kluyveromyces lactis

Spontaneously arising erythromycin-resistant mutants were isolated in the "petite-negative" yeast Kluyveromyces lactis. Two independently arising mutants were studied, in one erythromycin-resistance was conferred by a single dominant nuclear gene, and in the other the resistance was extrachromosomally inherited. In fermentable medium growth of sensitive and resistant strains in presence or absence of erythromycin does not qualitatively change the cytochrome absorption spectra, whereas oxygen uptake of parental strains growing in glucose-medium is affected by the drug. The importance of "petite-negative" yeasts like Kluyveromyces lactis for the study of nucleo-cytoplasmic interrelations is discussed.

The isolation and genetic characterization of extrachromosomal chloramphenicol and oligomycin-resistant mutants from the petite-negative yeast Kluyveromyces lactis

Spontaneous mutants of the petite-negative yeast Kluyveromyces lactis, resistant to the antibiotics chloramphenicol and oligomycin, were isolated and genetically characterized. Three chloramphenicol-resistant mutants showed non-Mendelian inheritance when crossed to sensitive parents. Of 5 oligomycin-resistant strains studied, three exhibited resistance due to the presence of an extrachromosomal mutation. The resistance of the other two deriving from a nuclear and recessive mutation. When two factor crosses in trans configuration were performed between two of the chloramphenicol and the five oligomycin-resistant mutants a polarity in recombination was observed with a predominance of sensitive (OSCS) over resistant (ORCR) reciprocal recombinants. Allelism tests carried out among the oligomycin-resistant mutants indicated the presence of at least two distinct extrachromosomal regions responsible for the resistance.

Nucleo-cytoplasmic interaction between oligomycin-resistant mutations in Saccharomyces cerevisiae

1.A single-gene nuclear mutant of Saccharomyces cerevisiae, isolated as oligomycin-resistant, exhibits in vivo cross-resistance to venturicidin and collateral sensitivity to Synthalin. All three compounds are inhibitors of mitochondrial oxidative phosphorylation. Oligomycin resistance and Synthalin sensitivity are recessive, while venturicidin resistance is dominant. 2. Acytoplasmic mutant, also isolated as oligomycin-resistant, shows collateral sensitivity to both Synthalin and venturicidin. All three traits undergo mitotic segregation in diploids formed by crossing mutant and normal halpoids. 3. A novel nucleocytoplasmic interaction is observed in diploids formed by crossing haploid strains containing the nuclear and the cytoplasmic mutations, respectively. The dominant venturicidin resistance determined by the nuclear gene undergoes mitotic segregation, which results from a suppression of the nuclear phenotype by the cytoplasmic mutation. When a diploid mitotic segregant contains primarily mutant-type mitochondria, venturicidin resistance is completely suppressed. In haploids containing both the nuclear and cytoplasmic mutations, suppression is only partial. 4. Oxidative phosphorylation and ATPase in mitochondrial fractions isolated fromcytoplasmic mutant cells are less sensitive to inhibition by oligomycin than normal, but in vitro sensitivity to venturicidin is not significantly changed. In similar mitochondrial fractions isolated from normal and nuclear mutant cells, no significant differences in sensitivity to either inhibitor are detected. 5. The molecular basis for the nucleocytoplasmic suppression of venturicidin resistance may involve participation of mitochondrial membrane, plasma membrane or both. Either mitochondria can undergo changes in venturicidin sensitivity upon isolation, or the molecular entity which controls access of venturicidin to the mitochondria resides outside of the organelles. 6. Our data establish that aspects of the response in vivo of both venturicidin and Snythalin are controlled by the mitochondrial genome. 7. The nucleocytoplasmic interaction described here is the first example in which a specific restricted mitochondrial mutation modifies the phenotypic expression of a nuclear gene.