The Effects of KU70 on Mitochondrial Stability in the Saccharomyces cerevisiae

Abstract

The purpose of this experiment is to determine the role of KU70, a nuclear gene, in maintaining mitochondrial DNA in the model organism Saccharomyces cerevisiae, the budding yeast. The mitochondrion is an organelle in eukaryotes that produces much of the ATP used by a cell. ATP, or adenosine-triphosphate, is a molecule within a cell that provides energy for cellular functions via its high energy holding phosphate bonds. Mitochondria have their own genomes, separate from nuclear DNA, which encodes many proteins needed for cellular respiration. Mutations can occur in the mitochondria of humans that could result in decrease or loss of mitochondrial function, which leads to neuromuscular or neurodegenerative diseases. The KU70 gene is actually a subunit of a heterodimer that works in coordination with KU80. These genes function in the stability of the genome during DNA double-strand break (DSB) repair through nonhomologous end-joining (NHEJ) and telomere maintenance. The goal of this project is to determine the effects caused by the loss of KU70 on the mitochondrial stability. By completing two different assays, respiration loss and direct repeat-mediated deletion (DRMD), the role of the gene can be predicted. The respiration loss assay showed a 1.4-fold decrease (p=0.027) in spontaneous respiration loss compared to the wild type strain. The rate of DRMD events in the nuclear and mitochondrial genomes showed 1.42-fold decrease (p= 0.014) in spontaneous mutation rates in nuclear DNA and a 1.69-fold decrease (p=0.075) in mitochondrial DNA compared to the wild type. Finally, the induced-DRMD assay showed a 1.23-fold decrease (p=0.029) in homologous recombination events compared to the wild type. These results suggest that Ku-independent end joining may be a more efficient repair pathway and promote mitochondrial stability.