The human UNG gene encodes both mitochondrial (UNG1) and nuclear (UNG2) forms of uracil-DNA glycosylase (UNG). These forms are generated from transcription from alternative promoters, promoter A and promoter B respectively, and the subsequent use of alternative splicing. UNG is responsible for the removal of uracil from DNA by hydrolysis of the N-glycosidic bond that links the base to the deoxyribose backbone, leaving an abasic site. UNG is a highly conserved enzyme found in many species.