Chart 1. (A) Structures of C, 5mC, 5hmC, 5fC, and 5caC and (B) Sequences and Numbering of the Nucleotides for DDD and Oxidized DDD Duplexesa.

^a In solution, the two strands of the DDD exhibit pseudo-dyad symmetry. NMR resonances of symmetry-related nucleotides in the two strands are not individually observed. In the crystal, corresponding nucleotides from paired strands are not symmetry-related, and nucleotides are numbered individually. DDD^m, DDD^hm, DDD^f, and DDD^ca refer to the DDD containing 5mC, 5hmC, 5fC, and 5caC, respectively.