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Since arsenite is known to induce oxidative DNA damage in human cells, we asked if it induces other types of DNA damage and how the DNA damage is repaired. Treatment of human promyelocytic leukemia NB4 cells with 0.5μM As2O3 for 30 min induced no DNA breaks, as analyzed by a standard comet assay. However, breaks were detected if these cells were then digested with endonuclease III (EnIII), formamidopyrimidine-DNA glycosylase (Fpg), or a nuclear extract (NE) of NB4 cells. Using either H2O2-Fe–treated nuclei or As2O3-treated cells, digestion with either NE or EnIII + Fpg generated the same amount of breaks, and subsequent treatment with EnIII + Fpg resulted in no increase in breaks in NE-digested cells and vice versa. The human cell lines, defective in nucleotide excision protein, such as xeroderma pigmentosum (XP) A, XPD, and XPG, excised Ultraviolet C-induced adducts less rapidly than normal fibroblasts, but excised As2O3 adducts at the same rate as the normal cells. Immunodepletion of the NE with antibody against 8-oxoguanine DNA glycosylase (OGG1) or MutY homolog (MYH) decreased the incision of As2O3-induced adducts, while antibodies against XPA, XPB, XPD, XPF, or XPG, did not. These results suggest that As2O3 induces the formation of only oxidative DNA adducts and that OGG1 and MYH are involved in this incision process.