5,6-saturated thymine lesions in DNA: Production by ultraviolet light or hydrogen peroxide

Thymine analogs with saturated 5-6 bonds are important types of DNA damage that are recognized by the DNA N-glyoosylase activity of E. coli endonu-clease III. Seeking agents which could preferentially form 5,6-hydrated thymine residues In duplex DNA both in vivo and In vitro, we exposed purified duplex DNA to 325- or 313-nm light; however, after such exposure pyrlmidine diners greatly predominated over 5,6-hydrated thymine. Hydrogen peroxide, on the other hand, formed significant numbers of endonuclease III-sensitive sites in vitro which were not apurinic/apyrimidinic lesions and thus were likely to be 5,6-hydrated thymines.