 The two DNA-binding motifs (a zinc finger and the H2TH (helix-two-turns-helix) motifs) suggest that the oxidised base is flipped out from double-stranded DNA in the binding mode and excised by a catalytic mechanism similar to that of bifunctional base excision repair enzymes.Fpg binds one ion of zinc at the C terminus, which contains four conserved and essential cysteines.Endonuclease VIII (Nei) has the same enzyme activities as Fpg above (,), but with a preference for oxidized pyrimidines, such as thymine glycol, 5,6-dihydrouracil and 5,6-dihydrothymine.