Figure 1.

Structures of Watson-Crick basepairs involving natural and modified nucleosides studied initially. Watson-Crick basepairing between A and T (A) D and T (B), G and C (C), and I and C (D), where A, T, G, C, I, and D indicate, respectively, 2′-deoxyadenosine, 2′-deoxythymidine, 2′-deoxyguanosine, 2′-deoxycytidine, 2′-deoxyinosine, and 2-amino-2′-deoxyadenosine (commonly designated by its base 2,6-diaminopurine). Glycosidic bonds to deoxyribose (dR) and hydrogen bonds (dashed lines) are shown. The minor groove appears at the bottom of each basepair.