Endo III, product of the nth gene, is an iron-sulfur containing DNA repair enzyme. It possesses DNA glycosylase activity with broad substrate specificity for mutated pyrimidine derivatives especially thymine glycol (Tg) but also for 5-hydroxycytosine and 5,6-dihydrothymine. In addition, it has an apurinic/apyrimidinic (AP) lyase activity which cleaves the DNA backbone by β elimination. Endo III protects E. coli cells from radiation damage caused by x-ray and UV irradiation and its activity overlaps the activity of endonuclease VIII. When overexpressed, it can also protect E.coli cells from alkylation defects caused by methylmethanesulphonate.
