Inheritance of multiple drug resistance in Saccharomyces cerevisiae: linkage to leu1 and analyses of 2 micron DNA in partial revertants

Curing of Saccharomyces cerevisiae 2-μm DNA by transformation

A general procedure for the curing of 2-μm in Saccharomyces cerevisiae is described. The method is based on the displacement of endogenous 2-μm DNA by the recombinant plasmid pMP78-1, which carries the yeast leu2 gene and the 2 -μm DNA replicon, but cannot be maintained stably in a yeast cell without endogenous 2-μm DNA. After transformation with pMP78-1 cells are grown selectively to displace 2-μm DNA. During the non-selective growth which follows, plasmid pMP78-1 is lost and up to 100% of the cells completely lack plasmids. In conjunction with a kanamycin resistance marker, as present in plasmid pMP81, this method should be applicable to cure any wild-type yeast strain. The stability of recombinant plasmids in cir (+) and cir (0) strains has been compared.

Altered form of subunit 6 of mitochondrial ATP synthase complex in oligomycin-resistant mutants of Chinese hamster ovary cells

Using an antiserum generated against a synthetic peptide predicted from the DNA sequence of the ATPase 6 gene of the mitochondrial DNA, we demonstrate that mitochondria from two oligomycin-resistant Chinese hamster ovary cell lines with a defined mutation in the ATPase 6 gene synthesize an altered ATPase 6 gene product. This altered gene product migrates in sodium dodecyl sulfate-polyacrylamide gels as if it has a molecular mass that is larger by 1000 daltons than the wild-type ATPase 6 gene product. We also demonstrate that mitochondria from four other independently isolated oligomycin-resistant Chinese hamster ovary mutant cell lines contain a similar altered ATPase 6 gene product. These results suggest that all six oligomycin-resistant cell lines have a similar mutation in the ATPase 6 gene of the mitochondrial DNA that encodes subunit 6 of the ATP synthase complex.

Genetic mapping of nuclear mucidin resistance mutations in Saccharomyces cerevisiae. A new pdr locus on chromosome II

In the yeast Saccharomyces cerevisiae, two nuclear pleiotropic drug resistance mutations pdr3-1 (former designation mucPR) and pdr3-2 (former designation DRI9/T7) have been selected as resistant to mucidin and as resistant to chloramphenicol plus cycloheximide, respectively. The pdr3 mutations were found not to affect the plasma membrane ATPase activity measured in a crude membrane fraction. Meiotic mapping using strains with standard genetic markers revealed that mutation pdr3-1 is centromere linked on the left arm of chromosome II at a distance of 5.9 +/- 3.3 cM from its centromere and 11.6 +/- 3.1 cM from the marker pet9. The centromere linked pdr3-2 mutation exhibited also genetic linkage to pet9 with a map distance of 9.8 +/- 3.2 cM. These results indicate that pdr3-1 and pdr3-2 are alleles of the same pleiotropic drug resistance locus PDR3 which is involved in the control of the plasma membrane permeability in yeast.

Two cytoplasmically inherited oligomycin-resistant Chinese hamster cell lines exhibit an altered mitochondrial translation product

Mitochondria from two different cytoplasmically inherited oligomycin-resistant Chinese hamster ovary cell lines synthesize an altered polypeptide compared to mitochondria from wild-type cells. For example, mitochondria from both oligomycin-resistant cell lines synthesize a polypeptide with a molecular weight of approximately 20,500, which is present in very low amounts in wild-type cells. In contrast, mitochondria from wild-type cells synthesize a polypeptide with a molecular weight of approximately 19,500, which is present in very low amounts in one of the oligomycin-resistant mutants and in reduced amounts in the other mutant. The gene which encodes this altered polypeptide is cytoplasmically transferred together with the oligomycin-resistant phenotype. This is the first example in mammalian cells where an altered mitochondrial gene product is shown to be associated with the cytoplasmic transfer of oligomycin resistance.

Influence of the membrane on T-2 toxin toxicity in Saccharomyces spp

In growing cells of Saccharomyces cerevisiae and Saccharomyces carlsbergensis, T-2 toxin inhibits cell growth. We have examined the role of the yeast membranes in the uptake mechanism(s) of T-2 toxin. The effects of membrane-modulating agents, ethanol, cetyltrimethylammonium bromide, Triton X-100, and heat were studied; these agents were found to increase the sensitivity of the yeasts toward T-2 toxin. In the presence of 5% (vol/vol) ethanol, 2 micrograms of T-2 toxin per ml caused complete inhibition of growth. In the presence of 1 microgram of cetyltrimethylammonium bromide per ml, yeast cells became sensitive to T-2 toxin, starting with a concentration of 0.5 micrograms/ml. Triton X-100 at concentrations below 1% (vol/vol) sensitized the cells toward T-2 toxin, but at higher concentrations it protected the cells from T-2 toxin. Temperatures of incubation between 7 and 30 degrees C influenced the growth reduction caused by T-2 toxin. The greatest observed reduction of growth in T-2 toxin-treated cultures occurred at 30 degrees C. To further prove that the membrane influences the interaction of T-2 toxin with yeasts, we have studied a yeast mutant with a reduced plasma membrane permeability (G. H. Rank et al., Mol. Gen. Genet. 152:13-18, 1977). This yeast mutant proved to be resistant to T-2 toxin concentrations of up to 50 micrograms/ml. These results show that the membrane plays a significant role in the interaction of T-2 toxin with yeast cells.

Biochemical genetics of the mammalian oxidative phosphorylation system: analysis of the difference in the sensitivity of various Chinese hamster cell lines to inhibitors of the mitochondrial ATP synthase complex

Seven different Chinese hamster cell lines were found to vary greatly in their sensitivity to inhibitors of the mitochondrial ATPase. In plating-efficiency experiments, Chinese hamster lung V79 and bone marrow M3-1 cells were approximately 10,000-fold more resistant to oligomycin, 100-fold more resistant to efrapeptin, and 10-fold more resistant to ossamycin and leucinostatin than were ovary CHO or peritoneal B14 cells. In vitro experiments indicated that the increased resistance of V79 versus CHO cells to these inhibitors was due to an increased resistance of the mitochondrial ATPase. Heat-inactivation experiments indicated that there was a difference in the structure of the mitochondrial ATPase of V79 and CHO cells. Genetic experiments indicated that the difference in the sensitivity of V79 and CHO cells to inhibitors of the ATPase and the difference in the structure of the mitochondrial ATPase of V79 and CHO cells was due to a difference in both a nuclear and a cytoplasmic gene.

Maintenance of the 2 microns circle plasmid in populations of Saccharomyces cerevisiae

The 2 microns circle plasmid is maintained at high frequencies in populations of yeast cells. To find out how the plasmid is maintained, three forces were measured: the selective advantage or disadvantage conferred by 2 microns circles, the rate of generation of [Cir0] cells, and the rate of illegitimate transfer of 2 microns circles from cell to cell. It was found that under the conditions used, 2 microns circles confer a selective disadvantage of about 1%, that [Cir0] cells are generated at the rate of 7.6 x 10(-5) per [Cir+] cell per generation, and that illegitimate transfer of 2 microns circles occurs at a rate less than 10(-7) per recipient cell per generation. The most likely explanation of 2 microns circle maintenance is that the plasmid is sexually transmitted at such a rate that it spreads through populations despite selection against it.

Allelism of pleiotropic drug resistance in Saccharomyces cerevisiae

Allelism of pleiotropic drug resistant (pdr) mutants was evaluated by complementation tests, linkage to chromosome-VII centromere markers and response to a partial suppressor (sur). Complementation tests were confounded by incomplete dominance and somatic segregation. Phenotypic suppression by sur was observed for all mutant and wild type alleles and thus could not be used to distinguish alleles. Five different alleles were tentatively identified by their close linkage to leul; 88 tetrads from three factor crosses produced the following linkages--leul (4.7) pdrl (17.0) trp5. Resistance of DRI 9/T7, a [cir o] strain of French origin, was not inherited as an allele of pdr but was controlled by a different pleiotropic centromere linked gene. An evaluation of published data suggest that antl, AMYl, till, cyh3, BOR2, and axe1 may be alleles of pdr. Thus pdr appears to be an allele that influences permeability to many inhibitors.

Assignment of an oligomycin-resistance locus to human chromosome 10

An oligomycin-resistant variant of human fibrosarcoma HT1080 was isolated and characterized as nuclear and codominant. The mutant was stable, was not cross-resistant to respiratory inhibitors, and it contained a mitochondrial ATPase which was less sensitive to oligomycin. Hybrids formed between the human mutant and a mouse cell line expressed the resistance phenotype. By a detailed karyotypic analysis of these hybrids using trypsin-Giemsa banding it was found that resistance to oligomycin correlated with the retention of two human chromosomes 10. The hybrid lines contained only mouse mitochondrial DNA as shown by analyses of mitochondrially synthesized proteins and mitochondrial DNA. The study assigns an ATPase oligomycin-resistance locus to human chromosome 10 and suggests that mouse and human subunits can combine in a functional enzyme complex.

Saccharomyces cerevisiae plasmid, Scp or 2 mum: intracellular distribution, stability and nucleosomal-like packaging

Cell fractions from yeast strains known to harbor the plasmic 2 mum or Scp were treated with nucleases used to probe eukaryotic chromosome structure. Scp and subfragments were identified by hybridization to natural or cloned Scp probes according to Southern (34). Specificity was confirmed with non-Scp probes. Copy/haploid nuclear genome(n) was estimated from reconstructions at a resolution of 0.5/n. About 43-67% of the total cellular copy exists as nucleoprotein complexes which separate from other debris on isokinetic sucrose gradients with s-values of 67-110. These complexes are totally degraded by DNAase I. Digestion with micrococcal nuclease produced integral-sized fragments; they are not generated by direct mixing of pure Scp with nuclear chromatin from a[cir] strain. Initial digests gave a repeat of 168 +/- 3 base pairs (bp) for both Scp and nuclear nucleoprotein; advanced digests reduced the nuclear repeat relative to Scp by 8 bp. Of a potential 37 repeat units/plasmid, 31-32 were directly measured. A strain difference in Scp autodegradation was found. A partial nuclease resistant form was also demonstrated whose abundance was cell strain and growth stage dependent. Both Scp isomers exist in these complexes which are structurally similar to simian viral 40 minichromosomes.