Why Does TNA Cross-Pair More Strongly with RNA Than with DNA? An Answer From X-ray Analysis

The TNA twist: L‐α‐threofuranosyl (3′→2′) nucleic acid (TNA) residues adopt a C4′‐exo pucker when incorporated into an A‐ (left) or a B‐form DNA duplex (right). The resulting intranucleotide P⋅⋅⋅P distance in TNA is very similar to that in RNA (represented by a C3′‐endo puckered adenosine residue; green). The structural data explain earlier observations that TNA hydridizes more stably with RNA than with DNA and that RNA constitutes the better template for ligating TNA fragments.