@article{discovery1351727,
           pages = {1048 -- 1053},
          volume = {35},
            note = {{\copyright} 2007 The Author(s).

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.},
            year = {2007},
           title = {High-resolution crystal structure of the intramolecular d(TpA) thymine-adenine photoadduct and its mechanistic implications},
         journal = {NUCLEIC ACIDS RESEARCH},
           month = {January},
          number = {4},
          author = {Davies, RJH and Malone, JF and Gan, Y and Cardin, CJ and Lee, MPH and Neidle, S},
            issn = {0305-1048},
        abstract = {A high-resolution crystal structure is reported for d(TpA)*, the intramolecular thymine-adenine photoadduct that is produced by direct ultraviolet excitation of the dinucleoside monophosphate d(TpA). It confirms the presence of a central 1,3-diazacyclooctatriene ring linking the remnants of the T and A bases, as previously deduced from heteronuclear NMR measurements by Zhao et al. (The structure of d(TpA)*, the major photoproduct of thymidylyl-(3?-5?)-deoxyadenosine. Nucleic Acids Res., 1996, 24, 1554-1560). Within the crystal, the d(TpA)* molecules exist as zwitterions with a protonated amidine fragment of the eight-membered ring neutralizing the charge of the internucleotide phosphate monoanion. The absolute configuration at the original thymine C5 and C6 atoms is determined as 5S,6R. This is consistent with d(TpA)* arising by valence isomerization of a precursor cyclobutane photoproduct with cis-syn stereochemistry that is generated by [2 + 2] photoaddition of the thymine 5,6-double bond across the C6 and C5 positions of adenine. This mode of photoaddition should be favoured by the stacked conformation of adjacent T and A bases in B-form DNA. It is probable that the primary photoreaction is mechanistically analogous to pyrimidine dimerization despite having a much lower quantum yield.},
             url = {http://dx.doi.org./10.1093/nar/gkl1101}
}