Biogenesis of mitochondria. 30. An analysis of polarity of mitochondrial gene recombination and transmission

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.

Fine structure of the 21S ribosomal RNA region on yeast mitochondrial DNA. III. Physical location of mitochondrial genetic markers and the molecular nature of omega

1. We have determined the physical location of mitochondrial genetic markers in the 21S region of yeast mtDNA by genetic analysis of petite mutants whose mtDNA has been physically mapped on the wild-type mtDNA. 2. The order of loci, determined in this study, is in agreement with the order deduced from recombination analysis and coretention analysis except for the position of omega+: we conclude that omega+ is located between C321 (RIB-1) and E514 (RIB-3). 3. The marker E514 (RIB-3) has been localized on a DNA segment of 3800 bp, and the markers E354, E553 and cs23 (RIB-2) on a DNA segment of 1100 base pairs; both these segments overlap the 21S rRNA cistron. The marker C321 (RIB-1) has been localized within a segment of 240 bp which also overlaps the 21S rRNA cistron, and we infer on the basis of indirect evidence that this marker lies within this cistron. 4. In all our rho+ as well as rho- strains there is a one-to-one correlation between the omega+ phenotype, the ability to transmit the omega+ allele and the presence of a mtDNA segment of about 1000 bp long, located between sequences specifying RIB-3 and sequences corresponding to the loci RIB-1 and RIB-2. This segment may be inserted at this same position into omega- mtDNA by recombination. 5. The role which the different allelic forms of omega may play in the polarity of recombination is discussed.

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.

Mitochondrial recombination in crosses of iso- and anisomitochondrial Saccharomyces cerevisiae

Mitochondrial mutants resistant to erythromycin, neomycin and monomycin were isolated. Mitochondria were transmitted from different natural strains to the cells of the same nuclear genotype. In bifactorial crosses of such isochromosomal and anisomitochondrial yeasts we tested random samples of diploid colonies. The distribution of mitochondrial markers in parent and recombinant classes has been shown to occur unequally. The asymmetry of parent and the polarity of recombinant classes were observed to differ in different mitochondrial mutants. Anisomitochondrial strain crosses proved that mitochondrial origin essentially influenced both the parent and recombinant classes distribution and the susceptibility of the transmission to the effect of mating type locus. One can distinguish between 'homo- and heterosexual' cross combinations in terms of recombination polarity. The new type of mitochondria was found to occur with high frequency of transmission to the zygote progeny of markers resistant to erythromycin but not of markers resistant to neomycin. The problem of 'sex' in mitochondria is discussed.

Effects of elevation of strain-ploidy on transmission and recombination of mitochondrial drug resistance genes in Saccharomyces cerevisiae

In order to study the effects of strainploidy on the transmission and recombination of the mitochondrial genes C, E and O conferring the resistance to chloramphenicol, erythromycin and oligomycin, respectively, haploids were crossed to diploids and the results of genetic analysis were compared with those from haploid X haploid crosses. All haploid X haploid crosses showed an increased transmission of diploid derived alleles, relative to haploid derived ones, but the pattern of increase differed between homosexual and heterosexual crosses. In omega-haploid X omega-diploid homosexual crosses, the increase was of roughly equal magnitude at the C, E and O LOCI: there was a polar co-transmission of the diploid derived alleles. In omega plus haploid by omega-diploid heterosexual crosses, on the contrary, a differential increase was observed at the different loci, the magnitude being the smallest at the C locus and the largest at the O locus. As a result, there was a preferential transmission in favor of the haploid derived C alleles and of the diploid derived O alleles. A near equal transmission from both parents was observed for the E alleles. A decrease and an increase in the recombination frequency were noticed in the above haploid by diploid homosexual and heterosexual crosses, respectively. The above phenomena were ascribed to different dosages of mitochrondrial genomes from parents. Experimental data were well accorded with the theoretical expectation which were obtained on the assumptions that diploids contain twice as many mitochondrial genomes as haploids, and that random pairings and recombination would occur among mitochrondrial genomes from parents. The elevation of strain-ploidy did not affect the recombination polarity which is under the control of the omega gene. It was theoretically predicted that a preferential transmission in favor of diploid derived alleles at all the C, E and O loci would be seen in omega-haploid x omega plus diploid heterosexual crosses as well as in omega plus haploid x omega plus diploid homosexual crosses, but that the magnitude of the polar transmission would vary depending upon the loci in the former crosses, while it would be the same at all the loci in the latter ones. The recombination frequency was predicted to decrease in both of these crosses.

Biogenesis of mitochondria. XLII. Genetic analysis of the control of cellular mitochondrial DNA levels in Saccharomyces cerevisiae

The proportion of total cell DNA which is mitochondrial DNA was measured in haploid, diploid and tetraploid strains of S. cerevisiae grown under a standard set of conditions. For all strains tested the mitochondrial DNA level was in the range 16%-25% of total cell DNA. Repeated measurements of the cellular level of mitochondrial DNA in two haploid strains showed that these strains have measurably different cellular mitochondrial DNA levels (17% and 24% of total DNA, respectively) under our conditions. These two grande strains were used to investigate the role of the mitochondrial and nuclear genomes in the regulation of the mitochondrial DNA level. We have shown by genetic analysis that the difference between these two strains is determined by at least two nuclear genes. The mitochondrial genome is not involved in the regulation of cellular mitochondrial DNA levels. A number of purified petite clones derived from independent spontaneous petite isolates of the grande strain which contained 24% mitochondrial DNA were also studied. The mitochondrial DNA levels in all but one of these petites fell in the range 20-25% of total cell DNA. From these results we conclude that, in general, the mitochondrial DNA level in petite strains is controlled by the same mechanism as operates in grande strains. We propose a general model for the control of the cellular mitochondrial DNA level, in which the amount of mitochondrial DNA per cell is determined by regulation of the number of mitochondrial DNA molecules per cell. This regulation is mediated through the availability of a set of nuclear coded components, possibly a mitochondrial membrane site, which are required for the replication of mitochondrial DNA.

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 petite mutants of Saccharomyces cerevisiae: transmissional types

We have studied a number of petite [rho-] mutants of Saccharomyces cerevisiae induced in a wild-type strain of mitochondrial genotype [ome- CHL(R) ERY(S) OLI(S) (1, 2, 3) PAR(S)] by Berenil and ethidium bromide, all of which have retained two mitochondrial genetic markers, [CHL(R)] and [ERY(S)], but have lost all other known markers. Though stable in their ability to retain these markers in their genome, these mutants vary widely among themselves in suppressiveness and in the extent to which the markers are transmitted on crossing to a common wild-type tested strain. In appropriate crosses all of the strains examined in this study demonstrate mitochondrial polarity, and thus have also retained the [ome-] locus in a functional form; however, five different transmissional types were obtained, several of them quite unusual, particularly among the strains originally induced by Berenil. One of the most interesting types is the one that appears to reverse the parental genotypes with [CHL(R) ERY(S)] predominating over [CHL(S) ERY(R)] in the diploid [rho+] progeny, rather than the reverse, which is characteristic of analogous crosses with [rho+] or other petites. Mutants in this class also exhibited low or no suppressiveness. Since all of the petites reported here are derived from the same wild-type parent, and so have the same nuclear background, we have interpreted the transmissional differences as being due to different intramolecular arrangements of largely common retained sequences.

Factors affecting petite induction and the recovery of respiratory competence in yeast cells exposed to ethidium bromide

When growing cultures of S. cerevisiae are treated with high concentrations of ethidium bromide (greater than 50 mug/ml), three phases of petite induction may be observed: I. the majority of cells are rapidly converted to petite, II. subsequently a large proportion of cells recover the ability to form respiratory competent clones, and III. slow, irreversible conversion of all cells to petite. The extent of recovery of respiratory competence observed is dependent on the strain of S. cerevisiae employed and the temperature and the carbon source used in the growth medium. The effects of 100 mug/ml ethidium bromide are also produced by 10 mug/ml ethidium bromide in the presence of the detergent, sodium dodecyl sulphate, and recovery is also observed when cells are treated with 10 mug/ml ethidium bromide under starvation conditions. Genetic analysis of strain differences indicates that a number of nuclear genes influence petite induction by ethidium bromide. In one strain, S288C, petite induction by 100 mug/ml ethidium bromide is extremely slow under certain conditions. Mitochondria isolated from from S288C lack the ethidium bromide stimulated nuclease activity found in D243-4A, a strain which shows triphasic kinetics of petite formation. This enzyme may, therefore, be responsible for the initial phase of rapid petite formation.

Meiosis in protists. Some structural and physiological aspects of meiosis in algae, fungi, and protozoa

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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.

Relative retention of mitochondrial markers in petite mutants: mitochondrially determined differences between RHO(+) strains

The relative frequency of retention of two mitochondrial loci, determining resistance to oligomycin (oli1) and erythromycin (ery1), has been analysed in petite (rho(−)) mutants derived from a number of unrelated strains ofSaccharomyces cerevisiae. The frequency of retention of one marker relative to the other in spontaneous petites showed marked variation dependent on the strain of origin. The differences between strains in this characteristic were shown to be mitochondrially determined. Further, for individual strains, the relative retention of the markers in petites derived after UV-irradiation varied considerably in several cases from that observed with spontaneous petites. The observations on relative marker retention and the varied effects of UV-irradiation are discussed in terms of possible structural differences in the mitochondrial genomes of the various strains.

Mesosomes: membranous bacterial organelles

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Three-marker extranuclear mitochondrial crosses in Aspergillus nidulans

Two- and three-point extranuclear crosses have been carried out via heterokaryons involving the three extranuclear mitochondrial markers of Aspergillus nidulans: (oliA1), (cs67) and (camA112). All three markers appear to be located on a single functional mitochondrial genome. Recombination between all three pairs of extranuclear markers appears to be equally frequent, suggesting a lack of genetic linkage. An important feature of these results is the variable and often marked non-equality of frequency of reciprocal classes of recombinants.

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.

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.

Genetic analyses of the polarity alleles in recombinants from mitochondrial genetic crosses

A number of minority recombinant and parental types from a heterosexual cross were analyzed for the omega allele they carry. It was found that recombinant progeny can be omega(-), that minority parental types among the progeny can be omega(+) rather than omega(-), and, finally, that certain of the results suggest that the omega locus may not be at the proximal end of the mitochondrial genetic map (Bolotin et al., 1971; Grivell et al., 1973) but rather may lie between the [cap1-r/cap-s] and [ery1-r/ery-s] loci.

Mitochondrial genetics, circular DNA and the mechanism of the petite mutation in yeast

We propose a general hypothesis involving properties of circular DNA which can explain such phenomena as thepetitemutation, suppressiveness, and the polarity observed in mitochondrial recombination in the yeastSaccharomyces cerevisiae. This hypothesis involves excision and insertion events between circular DNA molecules as well as structural rearrangements in the DNA generated by these events. The special properties of circular DNA have been considered in analysing recombination, and a number of results are obtained which are not intuitively apparent.

This hypothesis can be applied to any situation involving circular DNA such as bacterial plasmids and cytoplasmic circular DNAs, where the opportunity exists for recombination and rearrangement events.

Biogenesis of mitochondria. The effects of physiological and genetic manipulation of Saccharomyces cerevisiae on the mitochondrial transport systems for tricarboxylate-cycle anions

1. Kinetic and equilibrium parameters for the uptake of l-malate, succinate, citrate and alpha-oxoglutarate by fully functional mitochondria of Saccharomyces cerevisiae were determined. 2. The uptake of l-malate and succinate is mediated by a common carrier, and two other distinct carriers mediate the uptake of citrate and alpha-oxoglutarate. 3. The properties of the carrier systems for l-malate, succinate and citrate closely resemble those of mammalian mitochondria, but the alpha-oxoglutarate carrier differs from the mammalian system in minor respects. 4. The composition of the yeast mitochondria was extensively manipulated by (a) anaerobiosis, (b) catabolite repression, (c) inhibition of mitochondrial protein synthesis and (d) elimination of mitochondrial DNA by mutation. 5. The carrier systems for l-malate, succinate, citrate and alpha-oxoglutarate are essentially similar in the five different types of mitochondria. 6. It is concluded that all the protein components of the carrier systems for l-malate, succinate, citrate and alpha-oxoglutarate are coded by nuclear genes and synthesized extramitochondrially by cell-sap ribosomes.