Involved in base excision repair of DNA damaged by oxidation or by mutagenic agents. Acts as DNA glycosylase that recognizes and removes damaged bases. Has a preference for oxidized pyrimidines, such as thymine glycol, formamidopyrimidine (Fapy) and 5-hydroxyuracil. Has marginal activity towards 8-oxoguanine. Has AP (apurinic/apyrimidinic) lyase activity and introduces nicks in the DNA strand. Cleaves the DNA backbone by beta-delta elimination to generate a single-strand break at the site of the removed base with both 3'- and 5'-phosphates. Has DNA glycosylase/lyase activity towards mismatched uracil and thymine, in particular in U:C and T:C mismatches. Specifically binds 5-hydroxymethylcytosine (5hmC), suggesting that it acts as a specific reader of 5hmC. 2'-deoxyribonucleotide-(2'-deoxyribose 5'-phosphate)-2'-deoxyribonucleotide-DNA = a 3'-end 2'-deoxyribonucleotide-(2,3-dehydro-2,3-deoxyribose 5'-phosphate)-DNA + a 5'-end 5'-monophospho-2'-deoxyribonucleoside-DNA + H(+) During mitosis, associates with centrosomes and condensed chromatin. Ubiquitous. Up-regulated during S-phase. The edited form removes thymine glycol from duplex DNA 30 times more slowly than the form encoded in the genome, whereas editing enhances repair of the guanidinohydantoin lesion by NEIL1. The recoding site is a preferred editing site for the RNA editing adenosine deaminase ADAR1. Belongs to the FPG family. Erroneous CDS prediction.