Role of tyrosyl-DNA-phosphodiesterase I in mitochondrial DNA repair

Abstract

The mechanisms for DNA repair in mitochondria is an area in which there is limited knowledge in comparison to the DNA repair mechanisms that have been defined in the nucleus. Although it is understood that mitochondria have less DNA repair mechanisms than in the nucleus there is still a lot more scope for identifying new proteins involved in the repair of mitochondrial DNA (mtDNA). The main focus of this thesis was to attempt to determine whether there was presence and activity of a DNA repair enzyme in mitochondria, namely tyrosyl-DNA-phosphodiesterase 1 (TDP1), and if so what is the exact role of this enzyme in mtDNA repair. This enzyme has already been characterised as an single strand break repair (SSBR) enzyme in the nucleus, and a mutation in this gene can cause the autosomal recessive disorder spinocerebellar ataxia with axonal neuropathy 1 (SCAN1). The data in this thesis provides evidence for the presence and activity of TDP1 in mitochondria and that the function of this enzyme on mtDNA is most likely limited to the removal of mitochondrial topoisomerase 1 (TOP1mt). It has also been shown that phosphorylation of amino acid 81 of TDP1 does not facilitate its interaction with DNA ligase 3α in mitochondria and that there most probably no direct link between these enzymes in this organelle, unlike that found in the nucleus. This data indicates that there is still potential for identification of more enzymes that are involved in mtDNA repair.