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

Genetic conservation versus variability in mitochondria: the architecture of the mitochondrial genome in the petite-negative yeast Schizosaccharomyces pombe

The great amount of molecular information and the many molecular genetic techniques available make Schizosaccharomyces pombe an ideal model eukaryote, complementary to the budding yeast Saccharomyces cerevisiae. In particular, mechanisms involved in mitochiondrial (mt) biogenesis in fission yeast are more similar to higher eukaryotes than to budding yeast. In this review, recent findings on mt morphogenesis, DNA replication and gene expression in this model organism are summarised. A second aspect is the organisation of the mt genome in fission yeast. On the one hand, fission yeast has a strong tendency to maintain mtDNA intact; and, on the other hand, the mt genomes of naturally occurring strains show a great variability. Therefore, the molecular mechanisms behind the susceptibility to mutations in the mtDNA and the mechanisms that promote sequence variations during the evolution of the genome in fission yeast mitochondria are discussed.

Analysis of the mitochondrial and nuclear genomes of two basidiomycetes, Coprinus cinereus and Coprinus stercorarius

The mitochondrial and nuclear genomes of Coprinus stercorarius and C. cinereus were compared to assess their evolutionary relatedness and to characterize at the molecular level changes that have occurred since they diverged from a common ancestor. The mitochondrial genome of C. stercorarius (91.1 kb) is approximately twice as large as that of C. cinereus (43.3 kb). The pattern of restriction enzyme recognition sites shows both genomes to be circular, but reveals no clear homologies; furthermore, the order of structural genes is different in each species. The C. stercorarius mitochondrial genome contains a region homologous to a probe derived from the yeast mitochondrial var1 gene, whereas its nuclear genome does not. By contrast, the C. cinereus nuclear, but not mitochondrial, genome contains a region homologous to the var1 probe. Only a small fraction of either the nuclear or mitochondrial genomes, perhaps corresponding to the coding sequences, is capable of forming duplexes in interspecies solution reassociations, as measured by binding to hydroxylapatite. Those sequences capable of reassociating were found to have approximately 15% divergence for the mitochondrial genomes and 7%-15% divergence for the nuclear genomes, depending on the conditions of reassociation.

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.

Extrachromosomal mutator inducing point mutations and deletions in mitochondrial genome of fission yeast

We report the isolation and characterization of a mutator mutant in the fission yeast Schizosaccharomyces pombe. This mutator is of extrachromosomal, very likely mitochondrial, inheritance and acts exclusively on mitochondrial mtDNA. It greatly enhances the frequency of spontaneous mitochondrial drug-resistance mutants compared to the wild type, but it is not obligatory for their occurrence. In contrast, mitochondrial respiratory deficient mutants can only be isolated from mutator strains. It could be shown that this mutator induces point mutations as well as deletions in the mitochondrial genome which lead to respiratory deficiency. This mutator might prove to have a novel function encoded by the mtDNA.

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.