TDG is SUMOylated at lysine-330 with SUMO2,3 by UBE2I and perhaps another E3 ligase (Hardeland et al. 2002, Baba et al. 2006, Hendriks et al. 2014, Tammsalu et al. 2014). SUMOylation increases turnover of TDG with G:U substrate and abolishes activity with G:T substrate (Hardeland et al. 2002).