Circular molecules of heterogeneous size from mitochondrial fractions of the petite-negative yeast Schizosaccharomyces pombe

Isolation and characterization of mitochondrial DNA from the alkane yeast Saccharomycopsis lipolytica

Mitochondrial (mt) DNA of the alkane yeast, Saccharomycopsis lipolytica, was isolated. Its buoyant density in CsCl was found to be of 1.687 g/cm(3), indicating a GC content of 27.5% and its melting point Tm = 79.5 °C, indicating a GC content of 24.9%. The corresponding values for nuclear (n) DNA, are 1.709 g/cm(3) (GC: 49.5%) and Tm = 90.5 (GC: 51.7%) respectively. Electron microscopy revealed that mtDNA has a circular structure with a contour length of about 14.5 µm corresponding to 45.5 kb per molecule. The size estimated from restriction analyses performed with 7 endonucleases was 48.35 kb/molecule. A restriction map was constructed, using the cleavage data of 4 endonucleases.

The structure of mitochondrial DNA from the liverwort, Marchantia polymorpha

The structure of mitochondrial DNA (mtDNA) from cultured cells of the liverwort, Marchantia polymorpha, was analyzed by pulsed-field gel electrophoresis (PFGE) and moving pictures of the fluorescently labeled molecules. Previous electron microscopic analysis with this liverwort revealed a unique property among land plants: mtDNA circles of only one size, that of the 186 kb genome, with no subgenomic circles. Most of the mtDNA was immobile in PFGE and contained complex structures, larger than the genome size with a bright fluorescent node and multiple attached fibers. The mobile mtDNA was mostly linear molecules in monomeric to pentameric lengths of the unit genome that increased following mung bean nuclease digestion, with a corresponding decrease in the immobile fraction. From 0 to 5% of the mtDNA was found as circular molecules the size of the genome and its oligomers; no subgenome-sized circles were present. Radiolabeling revealed that mtDNA synthesis began soon after transfer of cells to fresh medium and most newly replicated mtDNA was immobile; the circular form of the genome was not rapidly labeled.

Reaching for the ring: the study of mitochondrial genome structure

The linear molecules that comprise most of the mitochondrial DNA (mtDNA) isolated from most organisms result from the artifactual degradation of circular genomes that exist within mitochondria. This view has been adopted by most investigators and is based on DNA fragment mapping data as well as analogy to the genome-sized circular mtDNA molecules obtained in high yield from animals. The alternative view that linear molecules actually represent the major form of DNA within mitochondria is supported by two observations; (1) over a 1000-fold range of genome size among fungi and plants we find the same size distribution of linear mtDNA molecules, and (2) linear mtDNA molecules much larger than genome size can be found for some fungi and plants. The circles that represent only a small fraction of the mtDNA obtained from most eukaryotes could be optional sequence forms unimportant for mitochondrial function; they may also participate in mtDNA replication. The circles might result from incidental recombination events between directly repeated sequences within or between tandemly arrayed genome units on linear mtDNA molecules.

Expression of cloned mitochondrial DNA from the petite negative yeast Schizosaccharomyces pombe in E. coli minicells

The minicell producing Escherichia coli strain D24 (lysogenic for phage lambda cI857) was transformed with the recombinant plasmid pDG3 containing the entire mitochondrial (mt) genome of the fission yeast Schizosaccharomyces pombe (S. pombe) cloned in the single BamHI-site of the E. coli plasmid pBR322 (Del Giudice 1981). By DNA-RNA hybridization it could be shown that the total mtDNA sequence of the plasmid pDG3 was transcribed in the E. coli minicells. The cloned mtDNA also directed the synthesis of at least five novel polypeptides with molecular weights between 7,200 and 34,000. When the minicell producing E. coli strain P678-54 was transformed with the hybrid plasmid pDG3, considerable portions of the inserted mtDNA sequences were deleted. One of the resulting plasmids (pDG4), lacking about two-thirds of the mtDNA sequence, directed the synthesis of new polypeptides in the range of 7,000 to 17,500 daltons. Another derivative of pDG3, the plasmid pDG5, containing one-sixth of the mtDNA sequence, directed the synthesis of at least three novel polypeptides. The mt origin of novel polypeptides coded by the hybrid plasmid pDG3 was demonstrated by use of antisera raised against total mitochondrial proteins from S. pombe and antisera against subunits II and III of cytochrome c oxidase from Saccharomyces cerevisiae (S. cer.).

Extrachromosomal inheritance of nalidixic acid resistance in the petite negative yeast Schizosaccharomyces pombe

Spontaneous mutants resistant to nalidixic acid (NAL) were isolated from the petite negative yeast Schizosaccharomyces pombe (S. pombe). One of these mutants, resistant to 200 micrograms/ml NAL, nalr-Y13, was characterized both genetically and biochemically. The extrachromosomal inheritance of this mutation was demonstrated both by mitotic segregation and by mitotic haploidization analysis. In the wild-type, NAL at a concentration of 100 micrograms/ml almost completely inhibits incorporation of [14C]adenine in total DNA as well as in mitochondrial DNA. In the NAL-resistant mutant both total DNA synthesis and mitochondrial DNA synthesis were resistant to the drug. These results are discussed in view of previously published findings on the close interaction between the two DNA synthesizing systems in S. pombe.

Cloning of mitochondrial DNA from the petite negative yeast Schizosaccharomyces pombe in the bacterial plasmid pBR322

The entire mitochondrial (mt) genome of the yeast Schizosaccharomyces pombe (S. pombe) was cloned in the BamHI site of the Escherichia coli plasmid pBR322. Three lines of evidence demonstrate that the complete mtDNA molecule was amplified without rearrangement or partial loss. First, restriction of the hybrid plasmid with BamHI led to the recovery of two fragments corresponding to the linearized plasmid and the BamHI-cut mtDNA. Second, restriction of cloned and native mtDNA with HindIII revealed identical fragments. Third, mitochondrial ribosomal RNA hybridized to the same HindIII fragments from cloned mtDNA and from mtDNA isolated from mitochondria.

Synthesis of mitochondrial DNA during the cell cycle of the petite negative yeast Schizosaccharomyces pombe

Synthesis of mitochondrial DNA (mitDNA) and nuclear DNA (nucDNA) during growth of synchronously dividing cultures of Schizosaccharomyces pombe (S. pombe) was followed by pulse labelling with radioactive adenine and determination of its rate of incorporation into total protoplast DNA and into the DNA of DNase-treated mitochondria at different stages of the cell cycle. It could be demonstrated that both mitDNA and nucDNA were synthesised discontinuously and at different points in the cell cycle.

Nucleo-cytoplasmic interactions in the petite negative yeast Schizosaccharomyces pombe. Inhibition of nuclear and mitochondrial DNA syntheses in the absence of cytoplasmic protein synthesis

In the petite positive yeast, Saccharomyces cerevisiae, cycloheximide selectively inhibits protein synthesis on cytoplasmic ribosomes, and, as a consequence, nuclear DNA synthesis. Mitochondrial DNA, however, is synthesized for 4-6 h after cessation of protein synthesis. In this paper we show that in contrast to Saccharomyces cerevisiae, synthesis of mitochondrial and nuclear DNA is tightly coordinated in the petite negative yeast Schizosaccharomyces pombe, since inhibition of cytoplasmic protein synthesis leads immediately to cessation of both nuclear and mitochondrial DNA synthesis.

2 micrometer covalently closed non-mitochondrial circular DNA in the petite-negative yeast Schizosaccharomyces pombe

A population of small covalently closed non-mitochondrial circular DNA molecules was isolated from the petite-negative yeast Schizosaccharomyces pombe. The mean length of these molecules, possessing the same density as nuclear DNA (1.695 g/cm3) is 1.95 +/- 0.18 micrometer. The presence of these minicircles in crude mitochondrial preparations indicates their tight association with mitochondrial particles. Their disappearance after DNase treatment of mitochondria demonstrates their extramitochondrial location.