Escherichia coli endonuclease III (EC 4.2.99.18) [1] is a DNA repair enzyme that acts both as a DNA N-glycosylase, removing oxidised pyrimidines from DNA, and as an apurinic/apyrimidinic (AP) endonuclease, introducing a single-strand nick at the site from which the damaged base was removed. Endonuclease III is an iron-sulfur protein that binds a single 4Fe-4S cluster. The 4Fe-4S cluster does not seem to be important for catalytic activity, but is probably involved in the proper positioning of the enzyme along the DNA strand [2]. The 4Fe-4S cluster is bound by four cysteines which are all located in a 17 amino acid region at the C-terminal end of endonuclease III. A similar region is also present in the central section of mutY and in the C-terminus of ORF-10 and of the Micro-coccus UV endonuclease [4].

1: Novel DNA binding motifs in the DNA repair enzyme endonuclease III crystal structure. Thayer MM, Ahern H, Xing D, Cunningham RP, Tainer JA; EMBO J. 1995;14:4108-4120. PMID:7664751

2: Cloning and expression of the cDNA encoding the human homologue of the DNA repair enzyme, Escherichia coli endonuclease III. Hilbert TP, Chaung W, Boorstein RJ, Cunningham RP, Teebor GW; J Biol Chem. 1997;272:6733-6740. PMID:9045706

3: Engineering functional changes in Escherichia coli endonuclease III based on phylogenetic and structural analyses. Watanabe T, Blaisdell JO, Wallace SS, Bond JP; J Biol Chem. 2005;280:34378-34384. PMID:16096281

4: Direct electrochemistry of endonuclease III in the presence and absence of DNA. Gorodetsky AA, Boal AK, Barton JK; J Am Chem Soc. 2006;128:12082-12083. PMID:16967954