Single-nucleotide base excision repair DNA polymerase activity in C. elegans in the absence of DNA polymerase β

The base excision DNA repair (BER) pathway known to occur in Caenorhabditis elegans has not been well characterized. Even less is known about the DNA polymerase (pol) requirement for the gap-filling step during BER. We now report on characterization of in vitro uracil-DNA initiated BER in C. elegans. The results revealed single-nucleotide (SN) gap-filling DNA polymerase activity and complete BER. The gap-filling polymerase activity was not due to a DNA polymerase beta (pol beta) homolog, or to another X-family polymerase, since computer-based sequence analyses of the C. elegans genome failed to show a match for a pol beta-like gene or other X-family polymerases. Activity gel analysis confirmed the absence of pol beta in the C. elegans extract. BER gap-filling polymerase activity was partially inhibited by both dideoxy-nucleotide and aphidicolin. The results are consistent with a combination of both replicative polymerase(s) and lesion bypass/BER polymerase pol theta contributing to the BER gap-filling synthesis. Involvement of pol theta was confirmed in experiments with extract from pol theta null animals. The presence of the SN BER in C. elegans is supported by these results, despite the absence of a pol beta-like enzyme or other X-family polymerase.