Enzymatic incorporation of a third nucleobase pair

DNA polymerases are identified that copy a non-standard nucleotide pair joined by a hydrogen bonding pattern different from the patterns joining the dA:T and dG:dC pairs. 6-Amino-5-nitro-3-(10-b-D-20-deoxyribofuranosyl)-2(1H)-pyridone (dZ) implements the non-standard ‘small ’ donor– donor–acceptor (pyDDA) hydrogen bonding pattern. 2-Amino-8-(10-b-D-20-deoxyribofuranosyl)-imidazo[1,2-a]-1,3,5-triazin-4(8H)-one (dP) imple-ments the ‘large ’ acceptor–acceptor–donor (puAAD) pattern. These nucleobases were designed to present electron density to the minor groove, density hypothesized to help determine specificity for polymerases. Consistent with this hypothesis, both dZTP and dPTP are accepted by many poly-merases from both Families A and B. Further, the dZ:dP pair participates in PCR reactions catal