Self-Repair of Thymine Dimer in Duplex DNA

Intrastrand dimerization of adjacent thymine residues is the predominate reaction of DNA under UV irradiation and contributes in part to the mutagenic power of sunlight. The chemical and physical basis for the nonrandom distribution of these dimers observed in polynucleotides is not well understood. A defined system of oligodeoxynucleotides used in this Communication demonstrates the influence of purines surrounding dimer sites. Sequences of 5‘-GTTG-3‘ and 5‘-ATTA-3‘ established the lowest and highest photostationary levels of dimer, respectively. Intermediate levels were observed for 5‘-GTTA-3‘ and 5‘-ATTG-3‘ although the 5‘-G suppressed dimer levels more effectively than the 3‘-G. These data are consistent with an intrinsic ability of DNA to promote dimer repair by transient charge-transfer from a neighboring G.