Synthesis of mitochondrial and nuclear DNA in anerobically grown yeast during the development of mitochondrial function in response to oxygen

Transcription of mutS and mutL-homologous genes in Saccharomyces cerevisiae during the cell cycle

Transcription of the Saccharomyces cerevisiae DNA mismatch repair genes PMS1, MSH2, and MSH6, a recently discovered homolog of the Escherichia coli mutS gene, was shown to be cell cycle regulated. In contrast, transcription of the MSH1, MSH3 and MLH1 genes was not regulated during the cell cycle. The MSH1 gene, which is thought to be involved in DNA mismatch repair in mitochondria, was also not induced under aerobic growth conditions. Regulation of the PMS1 gene was dependent on intact MluI cell cycle boxes, as demonstrated by analysis of a promoter mutant. Both reduced and increased expression of PMS1 resulted in a mitotic mutator phenotype. Analysis of mRNA levels was performed with a newly developed reverse transcription-PCR (polymerase chain reaction) approach using fluorescently labeled primers and an automated DNA sequencer for detection of PCR products.

Direct analysis and significance of cardiolipin transverse distribution in mitochondrial inner membranes

The distribution of cardiolipin across the inner mitochondrial membrane was directly determined by using the ability of the fluorescent dye 10-N-nonyl-3,6-bis(dimethylamino)acridine (10-N-nonyl acridine orange) to form dimers when it interacts with the diacidic phospholipid. Two independent methods were employed: (a) a spectrophotometric measurement of 10-N-nonyl acridine orange binding to isolated rat liver mitochondria, mitoplasts and inside-out submitochondrial particles, and (b) a flow-cytometric analysis of specific red fluorescence, emitted when two dye molecules are bound to one membrane cardiolipin; the stoichiometry of 10-N-nonyl acridine orange binding to phosphatidylserine and phosphatidylinositol, 1 mol dye/mol phospholipid, prevented dye dimerisation and subsequent red-fluorescence appearance. 57% total cardiolipin was present in the outer leaflets of inner membranes of isolated organelles, a distribution confirmed by saturation measurements for mitoplasts and inside-out submitochondrial particles. The same asymmetry was directly observed in situ with mitochondrial membranes of quiescent L1210 cells, and with mitochondrial membranes of respiring yeasts. Nevertheless, alterations in ATP synthesis and inhibition of mitochondrial protein synthesis revealed that cardiolipin distribution was apparently tightly correlated with mitochondrial membrane assembly and activity.

Replication and amplification of the small mitochondrial DNAs in a cell suspension of Black Mexican Sweet maize

The mitochondrial genome of Black Mexican Sweet (BMS) maize includes the principal genome and two transcriptionally active minicircular DNAs of 1913 and 1445 bp. A cell suspension of this line was used to study the biology and replication of the minicircular DNAs. Synthesis of the DNAs was measured by (32)P incorporation; all mitochondrial DNAs (mtDNAs) were synthesized rapidly during logarithmic growth phases, whereas no synthesis could be detected in stationary phase. When stationary phase cultures were placed in fresh medium and incorporation was measured over time, the 1.9-kb minicircle renewed (32)P incorporation prior to incorporation into the 1.4-kb minicircle, the principal mitochondrial genome, or the nuclear genome. Interestingly, plastid DNA renewed incorporation at the same time as the 1.9-kb minicircle. The early replication of the 1.9-kb minicircle relative to the other DNAs increased the copy number of this DNA relative to the other mitochondrial DNAs. The copy number of the minicircular DNAs also varied between leaf cells and the cell suspension. This indicates that components of the mitochondrial genome exhibit differential replication. The ability to follow replication of individual mitochondrial components makes this system valuable for studies of DNA replication.

A rapid procedure for the isolation of yeast mitochondrial DNA suitable for restriction fragment analysis

A method for the rapid isolation of mitochondrial DNA from the yeast Saccharomyces cerevisiae is described. Cells are first disrupted by vortexing with glass beads and the mitochondrial DNA is then extracted directly from the cell lysate by poly-L-lysine-kieselguhr-exchange chromatography. The method is unique from most other published procedures in that there is no requirement for the isolation of either a crude or purified mitochondrial preparation. Mitochondrial DNA isolated by this procedure is shown to yield restriction endonuclease fragment patterns identical to those obtained from DNA isolated by other previously reported procedures.

A correlation between ethidium bromide uptake and petite mutagenesis during the yeast cell cycle

The intracellular uptake of radioactively labeled ethidium bromide is shown to exhibit a periodic increase at the beginning of each cell cycle in synchronously growing cultures of the yeast, Saccharomyces cerevisiae. These peak rates of ethidium bromide uptake coincide in time with both new rounds of bud formation and the initiation of nuclear DNA synthesis during each cell cycle. Moreover, the peak rates of ethidium bromide uptake are also shown to be correlated in time with the maximum rate of petite mutagenesis induction by this drug during successive cell cycles.

Acute and chronic hypoxia in rats. I. Effect on organismic respiration, mitochondrial protein mass in liver and succinic dehydrogenase activity in liver, kidney and heart

The objective of this investigation was to characterize organismic, organ and mitochondrial alterations in rats over the course of 27 days at 0.4 atm. In the adjustment phase (day 1 through 5) a significant decrease in systemic oxygen uptake and body weight (23% of pre-altitude values) occurred. In the acclimating state (day 7 to 27) body weight was regained but oxygen consumption remained depressed. Hematocrit increased hyperbolically from 45% in 0-day rats to 79% in 27-day rats. Liver, kidney and heart weights and total organ protein paralleled the changes observed in body weight. Total organ succinic dehydrogenase activity showed a wave-like oscillation for liver and kidney; activity was decreased in both organs by day 5, showed a transient but significant increase on days 16 through 18 and a return to diminished activity on day 27. Succinic dehydrogenase activity for heart became depressed in the adjustment phase but showed a stable level comparable to pre-altitude values in the accliminating phase, days 7 through 27. Liver mitochondrial protein mass was unchanged from pre-altitude values on days 5 and 27 even though succinic dehydrogenase activity was significantly depressed. Therefore, the changes in succinic dehydrogenase activity are not representative of altered mitochondrial mass but suggest that mitochondrial function was altered.

Plasma membranes from cardiac cells in culture. Enzymatic radio-iodination, evaluation of preparation and properties of the sarcolema

Plasma membranes from heart (sarcolemma) were prepared by the method of Kidwai, A.M. (1975) Methods in Enzymology (Fleischer, S. and Packer, L., eds.), Vol XXXIA, pp. 134--144, Academic Press, New York). On many occasions the sarcolemmal fraction identified by the enzyme markers such as (Na+ + K+)-ATPase banded at heavier densities (d greater than 1.25 g/ml) than expected for plasma membrane (d less than 1.15 g/ml). Radio-iodination of the membrane was added as an independent marker and conditions for the reproducible preparation of the sarcolemma were studied. Cultured heart cells were enzymatically iodinated under conditions which did not affect viability and labeled primarily the sarcolemma. The distribution of radioactivity in homogenates of cultured cells on the density gradient corresponded to that of the enzymes' activity. The best sarcolemma preparation was obtained with 0.3 M KCl extraction of heart homogenates in the presence of 0.05 M pyrophosphate, especially if the salt was also present during the fractionation by density gradient centrifugation. Alterations in the density were also observed with erythrocytes and cultured liver cells' plasma membrane. The data suggests a meta-stable state of the plasma membranes due to handling or storage which could cause alterations of some of their physical properties (e.g. density).

Dependence of cytoplasmic on mitochondrial protein synthesis in K. Lactis CBS 2360. I. Biochemical analysis

In the "petite negative" yeast Kluyveromyces lactis (strain CBS 2360) growth is inhibited by the same Erythromycin concentrations on fermentable and non-fermentable carbon sources. The minimal inhibitory concentrations of Erythromycin does not affect respiration, but completely inhibits total aminoacid incorporation by the cells in conditions in which permeability effects can be ruled out. The effect of the antibiotic on the "in vitro" protein synthesis by cytoplasmic and mitochondrial systems shows that inhibition is effective only at the mitochondrial level. Results suggest that the inhibition of growth and of total protein synthesis is a consequence of the inhibition of mitochondrial protein synthesis.

Effect of auxotrophic starvation of mitochondrial marker transmission in the cdc8 mutant of Saccharomyces cerevisiae

Crosses were made using strains of S. cerevisiae which carried mitochondrial markers conferring resistance to erythromycin and chloramphenicol. The effect of auxotrophic starvation of one parent prior to mating on the transmission of its mitochondrial markers was studied in different crosses relative to the presence of the cdc8 nuclear mutation (a temperature-sensitive DNA replication). In crosses between two cdc8 mutant strains, auxotrophic starvation of one of the haploid parental stains prior to mating caused a marked decrease of its mitochondrial marker transmission to the diploid progeny of the cross. The transmission decreased as a function of the time of starvation. This effect was not observed in the cross between two wild type strains and in crosses of starved cdc8 phenotypic revertants with cdc8 mutant strains. Only a small, if any, effect of starvation on mitochondrial marker transmission was observed when starved cdc8 mutant strains were crossed either with their phenotypic revertants or with the wild-type strains. In one of the haploid parental strains the starvation increased the frequency of petites as a function of starvation time, while in the other this effect was not observed. In the progeny of cdc8 X cdc8 crosses (both in starvation experiments and in control crosses) an increased frequency of diploid petite cells accompanied by a decreased frequency of recombination between mitochondrial markers was noticed. The influence of the cdc8 mutation on the transmission of mitochondrial markers is discussed in terms of high frequency of p- molecule formation in cdc8 strains.

DNA-dependent DNA polymerase from yeast mitochondria. Dependence of enzyme activity on conditions of cell growth, and properties of the highly purified polymerase

The activity of DNA polymerase was determined in gradient-purified mitochondria from yeast cells grown under a variety of conditions. The specific enzyme activity was found to be dependent on the degree of aeration of the cells, and on the carbon source used for the medium. It was sensitive to glucose repression, and was enhanced about two-fold by the growth of yeast cells in the presence of ethidium bromide. Mitochondria DNA polymerase was highly purified and several properties were determined. Sucrose density gradient centrifugation, and dodecylsulfate-polyacylamide gel electrophoresis revealed the following structure: a monomer of molecular weight around 60 000 aggregated under relatively high salt concentration (0.2 M phosphate buffer) to a dimer of about 120 000 which under low salt concentration (0.2 M Tris-HCl buffer) formed higher aggregates. For optimal activity an Mg2+ ion concentration of 50 mM was found necessary, Mn ions did not promote activity at any concentration tested (0.5--50 mM). Indeed, if added to Mg2+-containing assays, Mn2+ strongly inhibited enzyme activity at low concentrations. This might be an explanation for the inducation of mitochondrial mutants in yeast cells grown in the presence of Mn2+ ions. Mitochondrial DNA polymerase activity was strongly inhibited by low concentrations of the -SH reagent p-chloromercuribenzoate, the nucleotide analogue cytosine arabinoside triphosphate also exerted an inhibitory effect. An about 50% decrease of activity was observed in the presence of 1 mM o-phenanthroline in assay mixture containing DNA at about the Km concentration. The enzyme preferred a gapped template primer, poly(dA) - (dT)10, over nicked DNA and was unable to use a polyribonucleotide template, poly(rA) - (dT)10. In the purest preparations no exonuclease activity could be detected.

Light-stimulated synthesis of chloroplast DNA

Light-stimulated chloroplast DNA synthesis was studied during chloroplast development in the absence of cell division and nuclear DNA synthesis. Incorporation of 32Pi was stimulated 10-15 fold, however, the ratio of chloroplast DNA to nuclear DNA remained constant. Isotope dilution experiments suggested that stimulated labeling of chloroplast DNA represented more efficient utilization of exogenously supplied Pi rather than stimulated turnover of chloroplast DNA. The low level of DNA synthesis and chloroplast development were resistant to nalidixic acid which inhibits semiconservative replication of chloroplast DNA.

Rearrangement of mitochondrial DNA molecules during the differentiation of mitochondria in yeast. II. - Labelling studies of the precursor product relationship

The length distribution in sucrose sedimentation gradient of the newly-synthesized pulse-labelled mitochondrial DNA has been established at an early stage of depression in wild type yeast (Saccharomyces cerevisiae). This stage corresponded to the beginning of mitochondrial differentiation. The radioactive DNA was longer (mean lengths 5, 10 and 22-25 mu) than the preexisting cold DNA (mean length 6.5 mu with two shoulders at 4 mum and 10 mum and one minor peak at 2-2.5 mum). These date confirm that the mean size of the different length populations of linear yeast mitochondrial DNA are under physiological control. Chase experiments were undertaken as follows. The yeast cells were uniformly prelabelled under anaerobiosis. Therefore the mitochondrial DNA molecules were short. Respiratory adaptation was performed in a cold medium and the lengthening process was induced. The specific activities of the long molecules made up during the respiratory adaptation did mot markedly differ from that of prelabelled DNA (decrease of specific activity less than 18 per cent). Molecules as long as 40 mum were also recorded. This lengthening seems to proceed through a non reciprocal exchange of polynucleotide stretches between preexisting molecules. We call it rearrangement. It occurs during the differentiation of mitochondria. Much of the mitochondrial DNA is maintained whereas a small amount of DNA is synthesized. This hypothesis is favoured by recent genetical and physical studies on mitochondrial recombination in yeast.

Rearrangement of mitochondrial DNA molecules during the differentiation of mitochondria in yeast. I.-Electron microscopic studies of size and shape

Size and shape of purified mitochondrial DNA was analyzed by electron microscopy as a function of mitochondrial differentiation. The mitochondrial DNA was extracted at fourth growth stages corresponding to different steps of mitochondria repression and depression. It was heterogeneous both in form and length. The size of linear molecules ranged from 1 mu to 25 mu but most of the molecules could be assigned into four Gaussian subpopulations with mean lengths of 2.2 mu to 4.0 mu, 6.0 mu and 10.0 mu. The circular molecules were all open and sized varied from 0.5 mu to 10 mu. Their length repartition was congruent with a logarithmic Gaussian distribution. The relative proportion of the different classes of molecules changed according to the stage of the growth cycle: during the repression most of the mitochondrial DNA molecules were short: the population of 2.2 mu was predominant. The longest linear molecules were observed during derepression where the populations of 4.0 mu and 10.0 mu were only found as well as the highest proportion of circular molecules. At the stationary phase the mitochondrial DNA became short again and the circles disappeared completely. The mitochondrial DNA extracted from a cytoplasmic "petite" was composed of linear and circular molecules. The linear molecules ranged from 0.1 mu to 32 mu and most of them could be assigned to two subpopulations of 1.3 mu and 4.2 mu. The circular molecules which accounted for 11 percent had contour lengths of 0.7 mu and 1.5 mu. The physiological meaning of the change in the relative proportion of different classes of mitochondrial DNA is discussed.

Regular arrangement of restriction sites in Drosophila DNA

When DNA of Drosophila melanogaster is digested to completion with Hemophilus aegyptius restriction endonuclease, the majority of the products are DNA segments whose lengths fits a random distribution with an average of 350 base pairs. However, some 10% of the DNA is recovered as various segments of discrete lengths, ranging from 30,000 to 365 base pairs. These segments arise from the regular spacing of the enzyme restriction sites in limited portions of the Drosophila genome. Three segments have been shown to originate from mitochondrial DNA, while all the others can be assigned to one or more isopycnic density classes of nuclear DNA. Five of the discrete fragments display modular lengths, each being an integral multiple of a 365 base pairs subunit. The relative frequencies of these multiple segments suggest that they are derived from DNA originally containing restriction sites every 365 base pairs, and that approximately 25% of these sites have been randomly inactivated.

Biosynthesis of branched-chain amino acids in yeast: effect of carbon source on leucine biosynthetic enzymes

The three enzymes in the leucine biosynthetic pathway of yeast do not exhibit coordinate repression and derepression in response to the carbon source available in the culture medium. Growth in an acetate medium results in derepression of the first enzyme in the pathway, alpha-isopropylmalate synthase, and repression of the second two enzymes, alpha-isopropylmalate isomerase and beta-isopropylmalate dehydrogenase, relative to the levels found in glucose-grown cells. The role of endogenous leucine pools as a mediator of these differences was investigated. The leucine pools did not differ significantly between acetate-grown and glucose-grown cells. However, an elevated endogenous leucine pool, caused by exogenous leucine in the growth medium, did decrease the rate of decay of alpha-isopropylmalate synthase activity observed when acetate-grown cells were shifted to glucose. Evidence is provided suggesting that an elevated endogenous leucine pool may increase the in vivo stability of alpha-isopropylmalate synthase under several different conditions. Studies on the kinetics of alpha-isopropylmalate synthase decay in vivo and sensitivity to leucine inhibition indicate that there are two classes of the enzyme in acetate-grown yeast cells.

Synthesis and degradation of mitochondrial components in hypertrophied rat heart

The accumulation of inner mitochondrial components of rat heart was studied 1 and 3 days after constriction of the ascending aorta of rats. By 1 day after aortic constriction, the activities of three mitochondrial respiratory enzymes/mg of cardiac homogenate protein were increased; after 3 days, specific activities had levelled off or decreased. Selective accumulation of inner mitochondrial membrane components 24h after aortic constriction was further indicated by increased left ventricular cytochrome c concentration (nmol/mg of protein). By 3 days after surgery, cytochrome c concentration was significantly diminished. Low-temperature spectroscopy of isolated mitochondria showed that the ratios of cytochromes c, b and a+a(3) remained unchanged after aortic constriction, suggesting that cytochrome c was a good indicator of the response of the other mitochondrial inner-membrane cytochromes as well. The effect of cardiac hypertrophy on the turnover of cytochrome c was also examined. Cytochrome c was labelled in its haem group with delta-amino[2,3-(3)H(2)]laevulinate 3 days before aortic constriction. By 1 day after surgery the total ventricular radioactivity in cytochrome c of aortic banded animals was significantly higher than in sham-operated controls, indicating a decreased degradation rate in the former during the first postoperative day. delta-Aminolaevulinate was shown to be a particularly suitable precursor for such turnover studies, since it results in rapid pulse-labelling of cytochrome c (peak activity in 90min), is rapidly removed from the precursor pool (t((1/2))=30min) and is not reutilized.

Cardiolipin content of wild type and mutant yeasts in relation to mitochondrial function and development

The phospholipid composition of various strains of the yeast, Saccharomyces cerevisiae, and several of their derived mitochondrial mutants grown under conditions designed to induce variations in the complement of mitochondrial membranes has been examined. Wild type and petite (cytoplasmic respiratory deficient) yeasts were fractionated into various subcellular fractions, which were monitored by electron microscopy and analyzed for cytochrome oxidase (in wild type) and phospholipid composition. 90% or more of the phospholipid, cardiolipin was found in the mitochondrial membranes of wild type and petite yeast. Cardiolipin content differed markedly under various growth conditions. Stationary yeast grown in glucose had better developed mitochondria and more cardiolipin than repressed log phase yeast. Aerobic yeast contained more cardiolipin than anaerobic yeast. Respiration-deficient cytoplasmic mitochondrial mutants, both suppressive and neutral, contained less cardiolipin than corresponding wild types. A chromosomal mutant lacking respiratory function had normal cardiolipin content. Log phase cells grown in galactose and lactate, which do not readily repress the development of mitochondrial membranes, contained as much cardiolipin as stationary phase cells grown in glucose. Cytoplasmic mitochondrial mutants respond to changes in the glucose concentration of the growth medium by variations in their cardiolipin content in the same way as wild type yeast does under similar growth conditions. It is concluded that cardiolipin content of yeast is correlated with, and is a good indicator of, the state of development of mitochondrial membrane.

Isolation of Saccharomyces cerevisiae mitochondrial formyltetrahydrofolic acid:methionyl-tRNA transformylase and the hybridization of mitochondrial fMet-tRNA with mitochondrial DNA

Formyltetrahydrofolic acid:methionyl-tRNA transformylase was isolated from Saccharomyces cerevisiae mitochondria and used to prepare yeast mitochondrial [(3)H]formylmethionyl-tRNA. This fMet-tRNA hybridizes with mitochondrial DNA but not with yeast nuclear or E. coli DNA. Unlabeled mitochondrial, but not extramitochondrial, tRNA competes in this reaction. tRNA was eluted from the hybrid and found to contain the label almost exclusively in fMet-tRNA. Yeast cytoplasmic fMet-tRNA formylated with Escherichia coli enzyme, and E. coli fMet-tRNA, do not hybridize with mitochondrial DNA. It is concluded that yeast mitochondrial tRNA(fMet) is a gene product of the mitochondrial genome.

Mitochondrial development in liver of foetal and newborn rats

THE DEVELOPMENT OF THE INNER MITOCHONDRIAL MEMBRANE IN FOETAL AND NEONATAL RAT LIVER WAS STUDIED BY FOLLOWING THREE PARAMETERS: (1) the activity of several respiratory enzymes in homogenates and purified mitochondria, (2) the spectrophotometric determination of cytochrome content in the mitochondria and (3) the cardiolipin content in both homogenates and purified mitochondria. Respiratory-enzyme activities of homogenates of foetal liver were one-quarter to one-twentieth of those of homogenates of adult liver, and the enzyme specific activities in purified mitochondria from foetal liver were one-half to one-eighth of those in mitochondria from adult liver. The cardiolipin content of liver homogenates increased approximately twofold during the development period, but there was no significant change in the cardiolipin content of purified mitochondria. It is concluded that cell mitochondrial content approximately doubles in the immediate postnatal period. There was no evidence for an increase in the relative amount of cristae protein in mitochondria during this period to account for increases in mitochondrial enzyme specific activity, since cardiolipin and cytochrome concentrations remained unchanged and electron micrographs revealed no differences. The cause of the lower respiratory-enzyme specific activity in foetal liver mitochondria is unclear. Qualitative differences in respiratory units in foetal and mature animals are suggested.

Genetic evidence for 'Darwinian' selection at the molecular level. II. Genetic analysis of cytoplasmically-inherited high and low suppressitivity in Saccharomyces cervisiae

A method was devised for the genetic analysis of cytoplasmically-inherited high and low suppressitivity in S. cervisiae thus enabling a test of the prediction, by the model of 'Darwinian' selection of mitochondrial DNA, that abnormal mitochondrial DNA of a high suppressitivity strain has a replicative advantage over abnormal mitochondrial DNA of a low suppressitivity strain. Support for the model was indicated by the ability of the suppressive factor resident in the high suppressitivity strain to control the phenotypic expression of suppressitivity in zygotes formed by crossing a low and high suppressitivity strain.