Reversible Covalent Stabilization of Stacking Contacts in DNA Assemblies.

Stacking bonds formed between two blunt-ended DNA double helices can be used to reversibly stabilize higher-order complexes that are assembled from rigid DNA components. Typically, at low cation concentrations, stacking bonds break and thus higher-order complexes disassemble. Herein, we present a site-specific photochemical mechanism for the reversible covalent stabilization of stacking bonds in DNA assemblies. To this end, we modified one blunt end with the 3-cyanovinylcarbazole ( K) moiety and positioned a thymine residue (T) at the other blunt end. In the bound state, the two blunt-ended helices are stacked together, resulting in a co-localization of K and T. Such a configuration induces the formation of a covalent bond across the stacking contact upon irradiation with 365 nm light. This bond can also be cleaved upon irradiation with 310 nm light, allowing repeated formation and cleavage of the same covalent bond on the timescale of seconds. Our system will expand the range of conditions under which stacking-bond-stabilized objects may be utilized.