Recombinant Schizosaccharomyces pombe Nth1 Protein Exhibits DNA Glycosylase Activities for 8-oxo-7,8-dihydroguanine and Thymine Residues Oxidized in the Methyl Group

Abstract

Bacteria and eukaryotes possess redundant enzymes that recognize and remove oxidatively damaged bases from DNA through base excision repair. DNA glycosylases remove damaged bases to initiate the base excision repair. The exocyclic methyl group of thymine does not escape oxidative damage to produce 5-formyluracil (5-foU) and 5-hydroxymethyluracil (5-hmU). 5-foU is a potentially mutagenic lesion. A homolog of E. coli endonuclease III (SpNth1) had been identified and characterized in Schizosaccharomyces pombe. In this study, we found that SpNth1 recognizes and removes 5-foU and 5-hmU from DNA with similar efficiency. The specific activities for the removal of 5-foU and 5-hmU were comparable with that for thymine glycol. The expression of SpNth1 reduced the hydrogen peroxide toxicity and the frequency of spontaneous mutations in E. coli nth nei mutant. It was also revealed that SpNth1 had DNA glycosylase activity for removing 8-oxo-7,8-dihydroguanine (8-oxoG) from 8-oxoG/G and 8-oxoG/A mispairs. These results indicated that SpNth1 has a broad substrate specificity and is involved in the base excision repair of 8-oxoG and thymine residues oxidized in the methyl group in S. pombe.