Fig. 1. Proximal thymidines as sites for cross-linking in DNA nanostructures.

(A) Left: Chemical structures of two proximal thymidines before UV irradiation. Right: Schematic illustration of a six-helix bundle DNA nanostructure featuring single-stranded thymidines at strand termini (1), at half-crossovers (2), at full crossovers (3), and thymidine loops (4) before UV irradiation. (B) As in (A) but after exposure to light with 310-nm wavelength. CPD bonds are indicated as red ellipsoids.