Size and structural variations of mitochondrial DNA

Linear mitochondrial deoxyribonucleic acid from the yeast Hansenula mrakii

The mitochondrial deoxyribonucleic acid (mtDNA) from a petite-negative yeast, Hansenula mrakii, was studied. A linear restriction map was constructed with 11 restriction enzymes. The linearity of the genome was confirmed by direct end labeling of the molecule, followed by restriction analysis. The molecular weight of the DNA was found to be 55,000 base pairs. This is the first linear mtDNA found in yeast species. Using specific gene probes obtained from Saccharomyces cerevisiae mtDNA, we have constructed a gene map of H. mrakii mtDNA. The arrangement of genes in this linear genome was very different from the circular mtDNA of other known yeasts.

Anatomy of mitochondrial DNA from Paramecium aurelia

The linear genome of mitochondrial DNA from four species of Paramecium aurelia was investigated with respect to restriction endonuclease fragments, location and number of ribosomal RNA genes, and interspecies EcoRI and HindIII fragment homologies. One copy of each of the rRNA genes was found in all four species and the 14s and 20s rRNA genes were separated by at least 3,000 bp. R-Loop analysis of the 20s rRNA gene did not reveal the presence of an intervening sequence. Interspecies homology studies showed species 1, 5, and 7 to have a high degree of homology but species 4 was less than 50% homologous to species 1 mt DNA. For all four species, rRNA genes showed good homology indicating that these DNA sequences are highly conserved, even between species having many non-homologous regions. A major region of DNA which displayed little homology between species 1 and 4 was that fragment containing sequences essential for initiation of DNA replication.

Structure of mitochondrial DNA from Paramecium tetraurelia

Mitochondrial DNA (mtDNA) from endosymbiote-free stocks of Paramecium tetraurelia was isolated by 2 procedures. The buoyant density of the mtDNA in neutral CsCl was 1.702 gm/cm3, a value consistent with the melting temperature of the mtDNA. Only linear molecules were observed by electron microscopy. These molecules were homogeneous in size with a monomer molecular weight of 25.6 x 10(6) daltons. The size of the mtDNA determined after digestion with the restriction endonucleases EcoRI or Hind III agreed with the value obtained by electron microscopy. These studies also revealed that the digestion pattern of mtDNA from stock 172 differed from that of other 3 stocks (51, 127, 203) examined. Some mtDNA molecules exhibited snapback reassociation following denaturation.

Covalently closed, circular DNA in kappa endosymbionts of Paramecium

Caedobacter taeniospiralis(kappa), a bacterial endosymbiont isolated fromParamecium tetraureliastock 51, contains, in addition to the bacterial chromosome, covalently closed circular DNA molecules as shown by isolation on dye-buoyant-density gradients. The closed circular molecule has a contour length of 13·75 ± 0·04 µm with a buoyant density of 1·698 g/cm3. The buoyant density of the bacterial chromosome is 1·700–1·701 g/cm3. Kappa of the 51 group isolated from stock 298 and stock 6g2,P. tetraurelia, also contain the closed circular DNA. Two forms of kappa coexist in paramecia: brights and nonbrights. Examination by density-gradient centrifugation of the DNA of brights and nonbrights shows the extrachromosomal DNA to be associated mainly with brights. It is suggested that the extrachromosomal DNA might be the determinant for the refractile bodies and the helical phage-like structures found in brights.

Effect of chloramphenicol on replication of mitochondria in Tetrahymena

Tetrahymena pyriformis ST (3 X 10-4 cells/ml) was treated with 0.1 mg/ml chloramphenicol (CAP). Cell division ceased after 1.5 divisions with no decreased viability. Total mitochondrial volume and succinic dehydrogenase (SDH) activity/liter increased 1.7-fold and 3-fold, respectively. SDH activity/cell decreased whereas malate dehydrogenase activity/cell and respiratory control ratios and P:O ratios of isolated mitochondria were unchanged in treated cells. During 12 hours of growth in CAP the total surface area of mitochondrial inner and outer membrane was essentially unchanged or increased 4-fold, respectively. Mitochondria from cells treated with chloramphenicol had decreased size, buoyant density and protein:lipid ratio in the membranes. The membrane ubiquinone:protein ratio was unchanged. Tetrahymena cells contained 3.6 X 10-minus 12 g of mitochondrial DNA and 6,800 mitochondria in a volume of 41,000 mu-3. A 4-hour treatment with CAP caused a 4-fold increase in the number of mitochondria/cell and a 10-fold increase in mitochondria/liter in contrast to a 4-fold increase in number of mitochondria/liter in control cells. Thus CAP stimulated division of mitochondria. Individual mitochondria of treated cells had one-tenth the volume of control mitochondria. The rate of increase of mitochondrial DNA/liter was the same in control and CAP-treated cultures. The amount of DNA/mitochondrion decreased 75% in CAP-treated cells due to the rapid division of mitochondria. The cell volume, cell protein content and mitochondrial DNA content/cell decreased with growth of control cultures.

The molecular complexity of mu and pi symbiont DNA of Paramecium aurelia

The molecular size of mu and pi symbionts of Parameciumaurelia has been calculated from renaturation kinetic data. Observed values were 0.78 x 10(9) daltons for mu particle DNA and 0.81 x 10(9) daltons for pi particle DNA. Estimates of analytical complexity were 4.45 x 10(9) and 5.05 x 10(9) daltons respectively. Based on these data, mu and pi symbionts appear to possess multiple genomes and contain a minimum of 5 or 6 copies of each DNA sequence.

Physicochemical characterization of mitochondrial DNA from pea leaves

The mitochondrial DNA from pea leaves exists in a circular conformation. 25% of the circular molecules exist as supercoils, and 10% of the molecules are dimers. The molecular weight of mitochondrial DNA is about 66 to 70 x 10(6) by electron microscopy, and 74 x 10(6) from its renaturation kinetics. No evidence for inter- and intramolecular heterogeneity is found.

Circular chloroplast DNA from Euglena gracilis

Chloroplast DNA of the protozoan flagellate, Euglena gracilis, exists as circular molecules, 40 mum in contour length, as shown by electron microscopy and buoyant density analyses.

Mitochondrial deoxyribonucleic acid from Tetrahymena pyriformis and its kinetic complexity

1. Mitochondrial DNA from Tetrahymena pyriformis strain T has a buoyant density (rho) of 1.685 compared with rho1.688 for whole cell DNA. Mitochondrial preparations from T. pyriformis strain W show an enrichment of a light satellite (rho1.686), although this is not obtained free from nuclear DNA (rho1.692). 2. T. pyriformis mitochondrial DNA renatures rapidly and the kinetics of this process indicate a complexity of approx. 3x10(7) daltons. 3. The base-pairing in the renaturation product is of a precise nature, since the ;melting' temperature (80.5 degrees C) is indistinguishable from that of the native DNA (80.5 degrees C). 4. Centrifugation of mitochondrial DNA in an alkaline caesium chloride density gradient gives two bands, implying the separation of the complementary strands.

Nuclear and mitochondrial DNA from wild-type and petite yeast: circularity, length, and buoyant density

Purified mitochondrial and nuclear DNA from diploid isogenic wild-type and vegetative-petite baker's yeast were analyzed by electron microscopy and by analytical ultracentrifugation in CsCl gradients. The buoyant densities in CsCl of nuclear DNA were identical for the two strains (rho = 1.700), but there was a difference between mitochondrial DNA from the wild type (rho = 1.684) and the petite (rho = 1.680). Electron microscopy revealed both circular and linear filaments for nuclear and for mitochondrial DNA of both strains. Nuclear DNA molecules included 6.5 per cent cyclic filaments principally measuring 2 mu or less in contour length, and linear filaments showing a unimodal, disperse length-distribution centered at about 2 to 3 mu, for both strains. Mitochondrial DNA for wild type varied depending upon the method used to extract and purify the molecules; showing only 7.5 per cent circular molecules from CsCl-subfractionated samples, as compared with 15 per cent circles from chloroform-extracted DNA not subjected to CsCl and up to 50 per cent circles from osmotically-lysed mitochondira, as reported in an earlier study. Modal lengths of circles occurred at about 2, 5, and 10 mu Increasing shear degradation also was evident in comparisons of the length-distribution patterns of linear molecules using the three preparative methods. Petite mitochondrial DNA contained 36-38 per cent circular molecules which measured 0.3-5.3 mu, but principally in the range of 0.3 to 2.0 mu whether from chloroform-extracted populations or from ones subfractionated in CsCl. A previous study of osmotically lysed mitochondria had shown a maximum of 8 per cent circles, which we now attribute to a failure, at that time, to detect circles measuring less than 1 mu, a substantial component encountered in the purified DNA samples in the present study. Linear filaments presented a unimodal length distribution in every case. Despite the variation in molecule populations derived from the three different preparative methods, there were consistent differences between mitochondrial DNA from wild-type and petite yeast in frequencies and size of circular molecules, as well as in length distribution patterns.

Multiple amounts of DNA related to the size of chloroplasts : I. An autoradiographic study

Plants containing genetically small or large plastids appear in some euploid and trisomic types of Beta vulgaris.Small tissue samples of the first 6-10 leaves of nearly 30 euploid plants from 7 different generations were incubated in a solution containing (3)H-thymidine in dark/light cycles, for up to 72 hr. For semiquantitative autoradiography the chloroplasts were then prepared on the slides with various kinds of isolation media, and fixed with OsO4, glutaraldehyde, formaldehyde, or ethanol. The specifity of incorporation was tested by observing the extractability of label after differential treatment with acid or nucleases.Chloroplasts in leaves 2-11 cm long preferentially incorporate (3)H-thymidine. The silver grains over plastids appear to be in clusters (centres). A relationship between the number of grains and also between the number of centres on the one hand, and the chloroplast size on the other could be found.It is concluded that chloroplasts occur in various degrees of polyenergide organization, as has been described, for example, for blue-green algae. Regarding the presence and degree of polyploidy-the other form of genetic "polyvalency" -the experiments provided no information. A remarkable variation in chloroplast size (and number of labelled centres) was observed, not only between different plants or between different leaves of a plants, but also within small tissue samples.

Electron microscopy of the circular kinetoplastic DNA from Trypanosoma cruzi: occurrence of catenated forms

Circular kinetoplastic DNA was fractionated from Trypanosoma cruzi DNA by Hg-Cs(2)SO(4) gradient. Covalantly closed circular DNA was isolated by buoyant density centrifugation in ethidium bromide CsCl density gradients. Electron microscope studies have shown that kinetoplastic DNA molecules are in the form of open and closed circles of contour length 0.45 mu, the smallest known microbial DNA. DNA molecules are also in the form of catenanes consisting of two or more topologically interlocked circular units of the monomer size 0.45 mu. Associations of numerous circles have also been described and confirmed by band sedimentation. Long linear DNA molecules were also seen, their size ranging between 2 and 12 mu. These molecules are free or are attached to associations of circles.

Circularity of yeast mitochondrial DNA

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