UNG encodes one of several uracil-DNA glycosylases. One important function of uracil-DNA glycosylases is to prevent mutagenesis by eliminating uracil from DNA molecules by cleaving the N-glycosylic bond and initiating the base-excision repair (BER) pathway. Uracil bases occur from cytosine deamination or misincorporation of dUMP residues. Alternative promoter usage and splicing of this gene leads to two different isoforms: the mitochondrial UNG1 and the nuclear UNG2.the nuclear (UNG2) and mitochondrial (UNG1) isoforms of UNG result from alternative splicing and the use of alternative promoters. The UNG1 and UNG2 proteins contain different N-terminal sequences, but the downstream 269 amino acids are common and include a short region that binds replication protein A and a larger, compact catalytic domain.