Biogenesis of mitochondria 34. The synergistic interaction of nuclear and mitocohondrial mutations to produce resistance to high levels of mikamycin in Saccharomyces cerevisiae

Biogenesis of Mitochondria: Analysis of Deletion of Mitochondrial Antibiotic Resistance Markers in Petite Mutants of Saccharomyces cerevisiae

Yeast strains carrying markers in several mitochondrial antibiotic resistance loci have been employed in a study of the retention and deletion of mitochondrial genes in cytoplasmic petite mutants. An assessment is made of the results in terms of the probable arrangement and linkage of mitochondrial genetic markers. The results are indicative of the retention of continuous stretches of the mitochondrial genome in most petite mutants, and it is therefore possible to propose a gene order based on co-retention of different markers. The order par, mik1, oli1 is suggested from the petite studies in the case of three markers not previously assigned an unambiguous order by analysis of mitochondrial gene recombination. The frequency of separation of markers by deletion in petites was of an order similar to that obtained by recombination in polar crosses, except in the case of the ery1 and cap1 loci, which were rarely separated in petite mutants. The deletion or retention of the locus determining polarity of recombination (omega) was also demonstrated and shown to coincide with deletion or retention of the ery1, cap1 region of the mitochondrial genome. Petites retaining this region, when crossed with rho(+) strains, display features of polarity of recombination and transmission similar to the parent rho(+) strain. By contrast a petite determined to have lost the omega(+) locus did not show normal polarity of marker transmission. Differences were observed in the relative frequency of retention of markers in a number of strains and also when comparing petites derived spontaneously with those obtained after ultraviolet light mutagenesis. By contrast, a similar pattern of marker retention was seen when comparing spontaneous with ethidium bromide-induced petites.

The interaction of neuraminidase and hemagglutinin mutations in influenza virus in resistance to 4-guanidino-Neu5Ac2en

We have previously described a 4-guanidino-Neu5Ac2en (zanamivir)-resistant neuraminidase (NA) variant G70C4-G, with an active site mutation Glu 119 to Gly. This variant has been found to also harbor a hemagglutinin (HA) mutation in the receptor binding site, Ser 186 to Phe. Examination of early passages of the G70C4-G virus revealed that this HA mutation had arisen by the first passage. From a subsequent passage two transient variants were isolated which had each acquired a different second HA mutation, Ser 165 to Asn and Lys 222 to Thr. Both were highly drug resistant and drug dependent and their ability to adsorb to and penetrate cells was decreased. Comparison of drug sensitivities between the variant, with the additional HA mutation at Ser 165, and viruses with either mutation alone revealed that these two HA mutations acted synergistically to increase resistance. To determine the contribution to resistance of each of the NA and HA mutations in G70C4-G, the NA mutation was separated from the HA mutation by reassorting. The NA mutation and the HA mutation each conferred low-level resistance to zanamivir, while the two mutations interacted synergistically in the double mutant to give higher resistance in vitro. Infectivity was not adversely affected in the double mutant and while there was a small decrease in sensitivity to zanamivir in the mouse model, there was no detectable resistance to zanamivir in the ferret model.

Multiple drug resistance in the fission yeast Schizosaccharomyces pombe: evidence for the existence of pleiotropic mutations affecting dependent transport systems

The uptake of L-tyrosine into wild type and antibiotic resistant strains of Schizosaccharomyces pombe requires an energy source, is initially linear with respect to time, is inhibited by 2,4-dinitrophenol and sodium azide and is saturable. However the initial uptake rates and the amount of L-tyrosine accummulated by antibiotic resistant strains are much less than wild type. Comparison of the kinetic constants of uptake shows that mutant strains have a reduced maximum velocity of uptake compared to wild type and a larger Km. Since the three mutant strains possess a permeability barrier to L-tyrosine as well as being drug resistant this is an indication that antibiotic resistance may be caused by a decrease in plasma membrane permeability.

Suppression of mitochondrially-determined resistance to chloramphenicol and paromomycin by nuclear genes in Saccharomyces cerevisiae

Phenotypic "revertants" of a drug resistant strain of Saccharomyces cerevisiae were induced by mutgenesis with manganese. Several of these drug sensitive mutants have been shown to result from mutations in the nuclear genome that cause phenotypic modification (suppression) of the mitochondrially-determined drug resistant genotype. Four mutants carrying a single recessive nuclear gene capable of modifying mitochondrial chloramphenicol resistance are described; these may be assigned to three complementation groups. Chloramphenicol resistant mutants mapping at five separate mitochondrial loci are described. At least two of the nuclear genes cause modification of mitochondrial chloramphenicol resistance determined by mutations at three of these loci, but the other two loci are apparently non-suppressible by these nuclear alleles. This indicates that these modifiers do not act by causing a general decrease in cellular or mitochondrial permeability to the drug. A single dominant nuclear modifier of mitochondrial paromomycin resistance has been identified. It is non-allelic to and does not interact with the genes modifying mitochondrial chloramphenicol resistance.

Carbomycin resistance in mouse L cells

A mutant has been isolated from the mouse cell line LM(TK-) which is stably resistant to the macrolide antibiotic, carbomycin. Mitochondrial protein synthesis in this mutant was carbomycin resistant and chloramphenicol sensitive. Fusions between carbomycin-resistant and -sensitive cells produced hybrids, most of which were sensitive to 10 microgram/ml carbomycin. At 7.5 microgram carbomycin/ml, the average population resistance is low initially but increases with time. Carbomycin-resistant cells were enucleated and fused with carbomycin-sensitive cells under a variety of selective regimes designed to allow growth of carbomycin-resistant cytoplasmic hybrids (cybrids). No transfer of carbomycin resistance via the cytoplasm was detected. Karyoplasts from carbomycin-resistant cells showed a low transfer of resistance to 7.5 microgram carbomycin/ml in karyoplast-cell fusions. Carbomycin resistance in this mutant is therefore most likely encoded in a nuclear gene.

Nuclear-extranuclear interactions affecting oligomycin resistance in Aspergillus nidulans

The extranuclear mitochondrial oligomycin-resistant mutation of Aspergillus nidulans, (oliA1), was transferred asexually into four nuclear oligomycin-resistant strains of different phenotypes. In all four cases, the possession of the nuclear plus extranuclear mutation led to an increase in the in vivo level of oligomycin resistance. In two cases, the altered cytochrome spectrum and impaired growth ability determined by (oliA1) were suppressed by the nuclear mutations. In the third case, the in vitro oligomycin resistance of the double mutant ATPase was dramatically increased above that of either of the component single mutant strains, indicating a synergystic interaction between the nuclear and extranuclear gene products. In the fourth case, the double mutant became cold-sensitive. A new extranuclear mitochondrial oligomycin-resistant mutation (oliB332) is described. This mutant is phenotypically similar to, though not identical with, (oliA1) but is separable by recombination. A range of nuclear oligomycin-resistant mutants have been mapped. Despite presenting five distinctly different phenotypes, they all map at the same locus.

Biogenesis of mitochondria 48: mikamycin resistance in Saccharomyces cerevisiae--a mitochondrial mutation conferring resistance to an antimycin A-like contaminant in mikamycin

Commercial preparations of mikamycin have been shown to act as both inhibitors of mitochondrial protein synthesis and respiration. These preparations are shown to consist of two major streptogramin components (mikamycin A and mikamycin B) and a number of minor components. The major streptogramin components which inhibit mitochondrial protein synthesis in vitro are without effect in vivo due to whole cell impermeability to these compounds. A minor antimycin A-like component is the active compound in mikamycin preparations which inhibits growth of yeast cells on ethanol. The site of this inhibition is at the level of respiratory Comples III. The mitochondrial [mik 1-r] mutation confers resistance to this minor growth inhibitory component and cross resistance to antimycin A. For clarity the designation mik 1 has therefore been renamed ana 1 to denote the mitochondrial determinant conferring resistance to antimycin A. Genetic and physical mapping studies localise the ana 1 determinant in the region of mitochondrial DNA specifying cytochrome b. It is proposed that the ana 1 locus is part of a gene specifying a membrane component of Complex III.

Extra-chromosomal inheritance of rhodamine 6G resistance in Saccharomyces cerevisiae

Rhodamine 6G was found to be a specific inhibitor of aerobic growth of yeast, having no effect on fermentative growth. A single step spontaneous mutant of S. cerevisiae resistant to rhodamine 6G was isolated, which showed cross-resistance to the ATPase inhibitors venturicidin and triethyltin, to the uncoupler 1799, to bongkrekic acid and to cycloheximide, but not to oligomycin or to the inhibitors of mito chondrial protein synthesis, chloramphenicol and erythromycin. The genetic analysis of this mutant showed that both nuclear and cytoplasmic (but apparently not mitochondrial) factors may be involved in the determination of the mutation. The behaviour is discussed as a possible function for 2 micron circular (omicron) DNA.

Mucidin resistance in yeast. Isolation, characterization and genetic analysis of nuclear and mitochondrial mucidin-resistant mutants of Saccharomyces cerevisiae

Mutants of Saccharomyces cerevisiae resistant to the antibiotic mucidin, a specific inhibitor of electron transport between cytochrome b and c, were isolated and divided into three phenotypic groups, as follows. Class 1 mutants were cross-resistant to a variety of mitochondrial inhibitors and exhibited no resistance at the mitochondrial level. Class 2 mutants were specifically resistant to mucidin exhibiting resistance also at the level of isolated mitochondria. Biochemical studies indicated that the mucidin resistance in class 2 mutants involved a modification of mucidin binding of inhibitory sites on the mitochondrial inner membrane without a significance change in the sensitivity of mitochondrial oxygen uptake to antimycin A, 2-heptyl-4-hydroxyquinoline-N-oxide, and 2,3-dimercaptopropanol. Class 3 was represented by a mutant which showed a high degree of resistance to mucidin and was cross-resistant to a variety of mitochondrial inhibitors at the cellular level but exhibited only a resistance to mucidin at the mitochondrial level. Genetic analysis of mucidin-resistant mutants revealed the presence of both nuclear and mitochondrial genes determining mucidin resistance/sensitivity in yeast. Resistance to mucidin in class 1 mutants was due to a single-gene nuclear recessive mutation (mucPR) whereas that in class 2 mutants was caused by mutations of mitochondrial genes. Resistance in class 3 mutant was determined both by single-gene nuclear and mitochondrial mutations. In the mitochondrial mutants the mucidin resistance segregated mitotically and the resistance determinant was lost upon induction of petite mutation by ethidium bromide. Allelism tests indicated that the mucidin resistance mutations fell into two genetic loci (MUC1 and MUC2) which were apparently not closely linked in the mitochondrial genome. Recombination studies showed that the two mitochondrial mucidin loci were not allelic with other mitochondrial loci RIB1, RIB2 and OLI1. An extremely high mucidin resistance at the cellular level was shown to arise from synergistic interaction of the nuclear gene mucPR and the mitochondrial mucidin-resistance gene (MR) in a cell. The results suggest that at least two mitochondrial gene products, responsible for mucidin resistance/sensitivity in yeast, take part in the formation of the cytochrome bc1 region of the mitochondrial respiratory chain.

Biogenesis of mitochondria: molecular mapping of the mitochondrial genome of yeast

We have developed a new procedure for the detailed molecular mapping of any allele of the yeast (Saccharomyces cerevisiae) mitochondrial genome. The procedure employs a collection of different genetically characterized petite strains whose genomes have been physically defined by molecular hybridization. The map position of an allele is within the DNA segment common to all defined petites that can be shown by marker rescue to retain the locus. The same collection of petites can be used to locate the positions of mitochondrial rRNA and tRNA cistrons and DNA fragments produced by restriction endonucleases.

Biogenesis of mitochondria 44. comparative studies and mapping of mitochondrial oligomycin resistance mutations in yeast based on gene recombination and petite deletion analysis

A comparative study of eight independently isolated mitochondrial oligomycin resistant mutants obtained from three laboratories show a variety of phenotypes based on cross resistance to venturicidin and sensitivity to low temperature. Analysis of recombination between pairs of markers indicate the existence of at least three genetic classes; class A, cross resistant to venturicidin and including the mutations OIII, [olil-r], [olgi-R], [tso-r]; class B, mutations OI, [olil7-r], [OLG2-R]; and class C, the mutation O11. The recombination data is consistent with mutations of each class residing in three separate genes, although mutations of class A and B show very close linkage. Recombination in non-polar crosses had demonstrated that markers of all three classes are linked to the mikl locus in the configuration (AB)-mikl-C. The mapping of this segment with respect to other markers of the mitochondrial genome and the order of classes A and B was established by analysis of co-retention frequenceis of markers in primary petite isolates as well as by analysis of marker overlap of genetically and physically defined petite genomes. The unambiguous order eryl-A-B-mik1-C-par was obtained. DNA-DNA hybridization studies using mtDNA isolated from selected petites confirms this map and estimates the physical separation of markers. A resonable correlation exists in this region of th genome between distances estimated physically by hybridization and genetically by frequencey of recombination in non-polar crosses. It is potulated that the oligomycin-mikamycin linkage group represents a cluster of genes involved in determing a number of mitochondrial membrane proteins associated with the mitochondrial ATPase and respiratory complex III.

Genetic analysis of mitochondrial biogenesis and function in Saccharomyces cerevisiae

Different mitochondrial mutants have been isolated that affect mitochondrial ribosome function. These mutants were used to establish most of the known methods and principles of mitochondrial genetics in yeast. Another class of mitochondrial mutants have been shown to affect mitochondrial ATPase and, more specifically, the "membrane factor" of mitochondrial ATPase. These mutants might be very useful in studying the energy-conserving function, and the interaction between the hydrophobic and hydrophylic parts, of the ATPase complex. New types of mitochondrial point mutations, concerning cytochrome a-a3 or b, will soon open up new fields of investigation. The biochemical and genetic analysis of numerous mutants belonging to that category and recently obtained [31] is being currently pursued in Tzagoloff's and Slonimski's laboratories.

Molecular and genetic events accompanying petite induction and recovery of respiratory competence induced by ethidium bromide

The treatment of yeast cells with high levels of ethidium bromide causes a rapid induction of respiratory deficient mutants followed by a period of recovery to respiratory competence in 60 to 70% of the cells. Prolonged exposure then results in a final irreversible phase of petite formation. Sucrose gradient sedimentation analysis of 3H-adenine labelled mtDNA indicates that limited fragmentation (to about 16-18S) occurs during the initial phase of petite induction followed by a reassembly of the fragments during the period corresponding to the recovery of respiratory competence. The reassembly is associated with an ethidium bromide insensitive incorporation of 3H-adenine into mtDNA at a level consistent with repair synthesis. Genetic analyses, based on the transmission of five markers carried on the mtDNA of "repaired rho+" clones, suggests that reassembly occurs with a high degree of fidelity, though in two of a total of twenty five clones differences in marker transmission frequency were observed which could possibly reflect an altered gene order. In addition, a description is given of the marked changes in the suppressive nature of the treated cells and the temporary reduction in the capacity for marker transmission seen to accompany the transitory fragmentation of the mtDNA. The final phase of petite induction is an energy dependent degradation of the mtDNA to produce a rho degrees culture.

Mitochondrial genetics. XI. Mutations at the mitochondrial locus omega affecting the recombination of mitochondrial genes in Saccharomyces cerevisiae

1. A series of CS revertants has been selected from various strains (both omega+ and omega-) carrying a CR mitochondrial mutation at the RIB1 locus. The properties of mitochondrial recombination exhibited by these CS revertants in various crosses, have been examined systematically. The omega allele of the CS revertants has been defined in crosses with omega+ and omega- tester strains using two criteria: the polarity of recombination and a new criterium called relative output coefficient. We found that mutations of omega appear frequently associated with the mutations at the RIB1 locus selected from omega- strains but not with those selected from omega+ strains. A new allelic form of omega (omega n) which had not been found amongst wild type yeast strains is characterised. Similarly omega n mutation was found frequently associated with CR mutants at the RIB1 locus selected from omega- CS strains but not with those selected from omega+ CS strains. The omega n mutants, and the omega+ and omega- strains, explain the groups of polarity previously observed by Coen et al. (1970). 2. Main features of mitochondrial crosses with omega n strains (omega+ x omega n, omega- x omega n and omega n x omega n) are analysed. Recombination is possible between the different mitochondrial genetic markers. No high polarity of recombination is observed and the frequency of recombinants are similar to those found in homosexual crosses (omega+ x omega+ and omega- x omega-). A striking property, observed for the first time, exists in crosses between zota+ omega n CS strains and some zota- CREO mutants: the zota- CREO are unable to integrate by recombination their CR allele into the zota+ mit-DNA of omega n CS strains while being capable of integrating it into omega+ CS or omega- CS genomes. 3. It is proposed that the omega locus is the site of initiation of non reciprocal recombination events, the omega+/omega- pairing specifically initiates the non-reciprocal act while omega+/omega n or omega-/omega n pairings do not. 4. The molecular nature of the omega n mutation and its bearing on the structure of the omega locus are discussed. It is suggested that omega n mutations correspond to macrolesions (probably deletions) of a segment of the mit-DNA covering the omega and RIB1 loci. If omega n is a partial deletions of the omega- sequence the omega+ could be an additionnal deletion of the omega n sequence. 5. The occurrence of spontaneous CR and ER mitochondrial mutations has been analysed by the Luria and Delbrück fluctuation test in omega- and omega n isonuclear strains. Results of these tests indicate that an intracellular selection of resistant copies preexisting the action of the anttibiotic occurs.

Drug-resistant Leptomonas: cross-resistance in trypanocide-resistant clones

A Leptomonas of insect origin was highly susceptible to several standard trypanocides and leishmanicides in vitro. Resistance was induced to some of these drugs; clones were isolated from each strain. Cross-resistance patterns of the clones were derived for diamidines, quinapyramine (Antrycide), acriflavin, phenanthridines, and other drugs active against trypanosomes and leishmanias. Clones tested included two each that were resistant to acriflavin, Antrycide, diminazene aceturate (Berenil), and pentamidine and one that was resistant to stilbamidine. Appreciable cross-resistance was evident for all clones. Differences were observed between clones from the same parent strain. Collateral susceptibility towards isometamidium and oxophenarsine was detected in most clone-derived populations. In clones passaged without drug to test for drug fastness, acriflavin and pentamidine clones lost resistance within 10 transfers, whereas Berenil and Antrycide clones retained considerable resistance after 20 to 30 subcultures without drug. Considerations of differences in life cycles suggest that the clone collection may be useful in screening for agents effective against leishmanias and stercorarian trypanosomes rather than against salivary trypanosomes.

Cytoplasmic and nuclear mutations to chloramphenicol resistance in Aspergillus nidulans

Two chloramphenicol resistance mutations out of 123 tested in Aspergillus nidulans are inherited extranuclearly as judged by transmissibility in heterokaryons, lack of segregation at meiosis, and independent segregation from all of the eight nuclear linkage groups. They do not recombine with each other. However, experiments in collaboration with G. Turner and R.T. Rowlands show that they do recombine with cytoplasmic mutations to oligomycin resistance (Rowlands and Turner, 1973) and cold-sensitivity (Waldron and Roberts, 1973). These cytoplasmic chloramphenicol resistance mutations are stable and do not affect growth or morphology on antibiotic-free media. Nuclear mutations to chloramphenicol resistance map at a minimum of three loci. At one of these loci, most, but not all, mutations lead pleiotropically to cycloheximide hypersensitivity, and most of these, but not all, also confer pleiotropic hypersensitivity to salicylhydroxamic acid.

Biogenesis of mitchondria. Phospholipid synthesis in vitro by yeast mitochondrial and microsomal fractions

The ability in vitro of yeast mitochondrial and microsomal fractions to synthesize lipid de novo was measured. The major phospholipids synthesized from sn-[2-(3)H]glycerol 3-phosphate by the two microsomal fractions were phosphatidylserine, phosphatidylinositol and phosphatidic acid. The mitochondrial fraction, which had a higher specific activity for total glycerolipid synthesis, synthesized phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine and phosphatidic acid, together with smaller amounts of neutral lipids and diphosphatidylglycerol. Phosphatidylcholine synthesis from both S-adenosyl[Me-(14)C]methionine and CDP-[Me-(14)C]choline appeared to be localized in the microsomal fraction.