DNA Polymerase β Mediates Robust Base Lesion Repair in Mammalian Mitochondria

Mitochondrial genome integrity is fundamental to mammalian cell viability. Yet, mitochondrial DNA is constantly under attack from oxygen radicals released during ATP production. DNA repair is important in removing oxidatively‐induced base lesions in mitochondrial DNA, but the presence of a robust base excision repair system has remained unclear. Therefore, we addressed the questions of the presence and repair role of DNA polymerase β (pol β) in mitochondria of mammalian cells. Pol β was localized to mitochondria by electron microscopic immunogold staining and biochemical experiments. Extracts from mitochondria exhibited a strong base excision repair activity that was dependent on pol β. Mitochondria in pol β‐deficient mouse fibroblasts exhibited altered morphology by electron microscopy and were deficient in energy metabolism. These results indicate mammalian mitochondria have a robust base lesion repair system.