Identification of 5'-deoxyribose phosphate lyase activity in human DNA polymerase gamma and its role in mitochondrial base excision repair in vitro.

Mitochondria have been proposed to possess base excision repair processes to correct oxidative damage to the mitochondrial genome. As the only DNA polymerase (pol) present in mitochondria, pol gamma is necessarily implicated in such processes. Therefore, we tested the ability of the catalytic subunit of human pol gamma to participate in uracil-provoked base excision repair reconstituted in vitro with purified components. Subsequent to actions of uracil-DNA glycosylase and apurinic/apyrimidinic endonuclease, human pol gamma was able to fill a single nucleotide gap in the presence of a 5' terminal deoxyribose phosphate (dRP) flap. We report here that the catalytic subunit of human pol gamma catalyzes release of the dRP residue from incised apurinic/apyrimidinic sites to produce a substrate for DNA ligase. The heat sensitivity of this activity suggests the dRP lyase function requires a three-dimensional protein structure. The dRP lyase activity does not require divalent metal ions, and the ability to trap covalent enzyme-DNA complexes with NaBH4 strongly implicates a Schiff base intermediate in a beta-elimination reaction mechanism.