<p>This entry represents various uracil-DNA glycosylases and related DNA glycosylases (<db_xref db="EC" dbkey="3.2.2"/>), such as uracil-DNA glycosylase [<cite idref="PUB00000916"/>], thermophilic uracil-DNA glycosylase [<cite idref="PUB00042575"/>], G:T/U mismatch-specific DNA glycosylase (Mug) [<cite idref="PUB00008091"/>], and single-strand selective monofunctional uracil-DNA glycosylase (SMUG1) [<cite idref="PUB00042576"/>]. These proteins have a 3-layer alpha/beta/alpha structure. Uracil-DNA glycosylases are DNA repair enzymes that excise uracil residues from DNA by cleaving the N-glycosylic bond, initiating the base excision repair pathway. Uracil in DNA can arise either through the deamination of cytosine to form mutagenic U:G mispairs, or through the incorporation of dUMP by DNA polymerase to form U:A pairs [<cite idref="PUB00042578"/>]. These aberrant uracil residues are genotoxic [<cite idref="PUB00042577"/>]. The sequence of uracil-DNA glycosylase is extremely well conserved [<cite idref="PUB00001176"/>] in bacteria and eukaryotes as well as in herpes viruses. More distantly related uracil-DNA glycosylases are also found in poxviruses [<cite idref="PUB00004816"/>]. In eukaryotic cells, UNG activity is found in both the nucleus and the mitochondria. Human UNG1 protein is transported to both the mitochondria and the nucleus [<cite idref="PUB00004423"/>]. The N-terminal 77 amino acids of UNG1 seem to be required for mitochondrial localization, but the presence of a mitochondrial transit peptide has not been directly demonstrated. The most N-terminal conserved region contains an aspartic acid residue which has been proposed, based on X-ray structures [<cite idref="PUB00004202"/>] to act as a general base in the catalytic mechanism. </p>