Structural determinatlon of the ultraviolet light-induced thymine-cytosine pyrimidine-pyrimidone (6–4) photoproduct

Abstract
Ultraviolet light induces damage to DNA, with the majority of the damage expressed as the formation of cyclobutane dimers and pyrimidine-pyrimidone (6–4) photoproducts. The (6–4) photoproducts have been implicated as important UV light-induced premutagenic DNA lesions. The most abundant of the (6–4) products is the thymine-cytosine pyrimidine-pyrimidone (6–4) photoproduct, or TC (6–4) product. The structure of the TC (6–4) product was deduced by proton NMR, IR, and fast atom bombardment mass spectroscopy, and the product was found to differ from the previously described photoadduct, Thy(6–4)Pyo, by the presence of an amino group at the 5 position of the 5′ pyrimidine. The implications of this structure on DNA base pairing and the induction of ultraviolet light-induced mutations are discussed.