An enzyme (UNG, UDG, EC 3.2.2.-) that removes uracil in DNA that has arisen from deamination of cytosine or incorporation of dUMP instead of dTMP, thereby suppressing GC-to-AT transition mutations. There are two alternatively spliced isoforms, UNG1M (313 aa) in mitochondria and UNG1N in the nucleus. Defects in UNG1 are a cause of immunodeficiency with hyper-IgM type 5 syndrome because of impairment in the immunoglobulin (Ig) class-switching mechanism. A second gene encodes UNG2 (327 aa) which has no homology with UNG1 but homology with the conserved cyclin box region of several cyclins.
Subjects: Medicine and Health.