Mammalian base excision repair by DNA polymerases δ and ε

Abstract

Two distinct pathways for completion of base excision repair (BER) have been discovered in eukaryotes: the DNA polymerase β (Pol β )-dependent short-patch pathway that involves the replacement of a single nucleotide and the long-patch pathway that entails the resynthesis of 2-6 nucleotides and requires PCNA. We have used cell extracts from Pol β-deleted mouse fibroblasts to separate subfractions containing either Pol δ or Pol ε. These fractions were then tested for their ability to perform both short- and long-patch BER in an in vitro repair assay, using a circular DNA template, containing a single abasic site at a defined position. Remarkably, both Pol δ and Pol ε were able to replace a single nucleotide at the lesion site, but the repair reaction is delayed compared to single nucleotide replacement by Pol β. Furthermore, our observations indicated, that either Pol δ and/or Pol ε participate in the long-patch BER. PCNA and RF-C, but not RP-A are required for this process. Our data show for the first time that Pol δ and/or Pol ε are directly involved in the long-patch BER of abasic sites and might function as back-up system for Pol β in one-gap filling reactions.