NEIL1 (endonuclease 8-like protein 1), an enzyme with dual DNA glycosylase and beta/delta lyase activity, recognizes and binds DNA damage in the form of dihydrouracil (DHU) (Hazra et al. 2002). 5,6-dihydrouracil is a form of DNA damage produced by ionizing radiation under anoxic conditions, so that cytosine is deaminated and C5-C6 double bond in the pyrimidine ring is saturated with hydrogen. 5,6-dihydrouracil mispairs with adenine, leading to G:C -> A:T transitions (Dizdaroglu et al. 1993).