Adaptive expression responses in the Pol-γ null strain of S. pombe depleted of mitochondrial genome

Background: DNA polymerase gamma(Pol-gamma) has been shown to be essential for maintenance of the mitochondrial genome (mtDNA) in the petite-positive budding yeast Saccharomyces cerevisiae. Budding yeast cells lacking mitochondria exhibit a slow-growing or petite-colony phenotype. Petite strains fail to grow on non-fermentable carbon sources. However, it is not clear whether the Pol. is required for mtDNA maintenance in the petite-negative fission yeast Schizosaccharomyces pombe. Results: We show that disruption of the nuclear gene pog/(+) that encodes Pol-gamma is sufficient to deplete mtDNA in S. pombe. Cells bearing pog/Delta allele require substantial growth periods to form petite colonies. Mitotracker assays indicate that pog/Delta cells are defective in mitochondrial function and EM analyses suggest that pog/Delta cells lack normal mitochondrial structures. Depletion of mtDNA in pog/Delta cells is evident from quantitative real-time PCR assays. Genome-wide expression profiles of pog/Delta and other mtDNA-less cells reveal that many genes involved in response to stimulus, energy derivation by oxidation of organic compounds, cellular carbohydrate metabolism, and energy reserve metabolism are induced. Conversely, many genes encoding proteins involved in amino acid metabolism and oxidative phosphorylation are repressed. Conclusion: By showing that Pol-gamma is essential for mtDNA maintenance and disruption of pog/(+) alters the genome-wide expression profiles, we demonstrated that cells lacking mtDNA exhibit adaptive nuclear gene expression responses in the petite-negative S. pombe.