Abstract
8-oxoguanine (8-oxoG) is an abundant and critical base modification. It is excised from the DNA by MutM in Escherichia coli and Ogg1 in budding yeast and mammalian cells. However, any structural and functional homologs of them are not yet identified in Shizosaccharomyces pombe. Nth1 protein, an ortholog of E. coli Nth, was cloned from the S. pombe. It removes oxidative pyrimidines from the DNA. E. coli Nth and Nei remove 8-oxoG from the 8-oxoG:G mispairs in DNA. We examined whether the Nth1 protein functions as a DNA glycosylase/AP lyase for 8-oxoG in DNA as E. coli Nth and Nei. The Nth1 protein was expressed in E. coli and partially purified using glutathione affinity column chromatography. The DNA glycosylase activity was assayed for 8-oxoG:A, 8-oxoG:G or 8-oxoG:C containing duplex oligonucleotides. The Nth1 protein efficiently removed 8-oxoG from 8-oxoG:A and 8-oxoG:G pairs from DNA. The activity to remove 8-oxoG from 8-oxoG:A and 8-oxoG:G mispairs was much higher than that from 8-oxoG:C. Furthermore, we report about the effects of Nth1 expression on some mutator strains deficient in DNA N-glycosylases.
