Abstract
In living cells, various types of DNA damage are produced by reactive oxygen species and ionizing radiations. Most of oxidative DNA damage are primarily repaired by base excision repair (BER) system. DNA glycosylases excise damaged bases, releasing AP sites in the DNA. Then AP endonucleases and AP lyases cleave DNA, followed by repair synthesis and rejoining by DNA polymerases and DNA ligases. Most of all species so far examined have BER system. Therefore, BER plays an important role in maintenance of genome integrity. Endonuclease III (Nth) is a bifunctional glycosylase which excises oxidized pirimidines such as thymine glycol, and incises the resulting AP sites. The DNA glycosylase is conserved in many organisms, indicating that this enzyme plays an important role in removing oxidative damage from DNA. Neither OGG1 nor Nei homolog has been identified in C. elegans to remove oxdative base damage. Nth homolog is a major glycosylase to recognize and remove oxidatively damaged bases such as 8-oxoguanine in C. elegans. Recently, we cloned C. elegans nth homolog gene (Centh). In this study, we purified recombinant CeNth protein and examined the substrate specificity and reaction kinetics of CeNth.
