N-terminal domain of metazoan Nei-like glycosylase 3 (NEIL3)This family contains the N-terminal domain of the Metazoan Neil3. It belongs to the FpgNei_N, [N-terminal domain of Fpg (formamidopyrimidine-DNA glycosylase, MutM)_Nei (endonuclease VIII)] domain superfamily. DNA glycosylases maintain genome integrity by recognizing base lesions created by ionizing radiation, alkylating or oxidizing agents, and endogenous reactive oxygen species. They initiate the base-excision repair process, which is completed with the help of enzymes such as phosphodiesterases, AP endonucleases, DNA polymerases and DNA ligases. DNA glycosylases cleave the N-glycosyl bond between the sugar and the damaged base, creating an AP (apurinic/apyrimidinic) site. Most FpgNei DNA glycosylases use their N-terminal proline residue as the key catalytic nucleophile, and the reaction proceeds via a Schiff base intermediate. In contrast, mouse NEIL3 (MmuNEIL3) forms a Schiff base intermediate via its N-terminal valine. The latter is a functional DNA glycosylase in vitro and in vivo. MmuNEIL3 prefers lesions in single-stranded DNA and in bubble structures. In duplex DNA, it recognizes the oxidized purines spiroiminodihydantoin (Sp), guanidinohydantoin (Gh), 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG) and 4,6-diamino-5-formamidopyrimidine (FapyA), but not 8-oxo-7,8-dihydroguanine (8-oxoG). Since the expression of the MmuNeil3 glycosylase domain (MmuNeil3delta324) reduces both the high spontaneous mutation frequency and the FapyG level in a Escherichia coli mutant lacking Fpg, Nei and MutY glycosylase activites, NEIL3 may play a role in repairing FapyG in vivo. In addition to this MeNeil3_N domain, enzymes belonging to this family contain a helix-two turn-helix (H2TH) domain and a zinc finger motif, plus a characteristic C-terminal extension that contains additional zinc fingers. Neil3 is one of three homologs found in eukaryotes.