Fig. 5.

Recognition of the opposing G and the CpG context. In the product complex, hTDG^cat contacts the guanine positioned 3′ to the abasic nucleotide (3′-G, cyan) and the guanine across from the (THF) target site (i.e., the opposing G, magenta). hTDG^cat does not contact the cytosine partner of the 3′-G. The enzyme and DNA are rendered and colored as in Fig. 4. Dashed lines represent hydrogen bonds indicated by the structure. The N2H₂ and N1H of the opposing G are contacted by the backbone oxygen of A274 and P280, and the N2H₂ of the 3′-G is contacted by the Q278 side chain carbonyl and the A277 backbone amide (N–H bond vector nearly perpendicular to plane of 3′-G base).