Thionucleoside disulfide cross-linked duplex DNA

A strategy for covalent cross-linking of duplex oligonucleotides is described, and is based on a direct base-to-base disulfide bond formed by iodine oxidation of two appropriately positioned thionucleoside bases. Cross-link formation between 4-thio-2′-deoxyuridine and 6-thio-2′-deoxyinosine is demonstrated in three sequence contexts (3′ to 3′, 5′ to 5′, or opposed).