The Significance of the Nuclear Gene KU80 in Mitochondrial Genome Stability of Saccharomyces cerevisiae

Abstract

Mitochondria are essential organelles in eukaryotes. They are often referred to as the powerhouse of the cell because mitochondria manufacture ATP, which is required for the successful completion of many cellular processes. Mitochondria have individual genomes, separate from the nuclear DNA, which encode proteins required for respiration. In humans, mutations in the mitochondrial DNA (mtDNA) result in the loss of mitochondrial function which leads to neuromuscular and neurodegenerative disorders. The focus of this study is to determine the role of the nuclear gene KU80 in maintaining mtDNA stability in the budding yeast, Saccharomyces cerevisiae. The product of the KU80 gene is the protein, Ku80p. Ku80p, in humans, is encoded by the XRCC4 gene. Ku80p along with Ku70p forms a heterodimeric protein complex, which binds to DNA double-strand break ends and is required for the non-homologous end joining (NHEJ) pathway of DNA repair. The goal of this research is to determine whether loss of the KU80 gene plays a role in mitochondrial genome stability. Mitochondrial genome instability can arise via spontaneous point mutations or deletion events. Assays were performed to measure the spontaneous respiration loss rate between wild type and ku80-? mutant strains. The respiration loss assay showed a 1.90-fold increase (p=0.001256) in spontaneous respiration loss compared to the wild type strain. Strains were constructed to determine the role of KU80 in spontaneous direct-repeat mediated deletion (DRMD) events within the mitochondrial genome as well as the nuclear genome. The rate of DRMD events in the mitochondrial and nuclear genomes showed a 1.94-fold decrease (p=0.08711) in spontaneous mutation rates in mitochondrial DNA and a 5.87-fold decrease (p=0.000786) in nuclear DNA compared to the wild type. These results suggests that Ku80p plays a role in maintaining the integrity of the mitochondrial genome in budding yeast.