DNA photolyase repairs the trans-syn cyclobutane thymine dimer.

DNA photolyases catalyze the splitting of the cyclobutane ring joining the two dihydropyrimidines of a pyrimidine dimer by a photoinduced electron-transfer reaction. Previous studies concluded that photolyase repairs only the cis-syn form of the eight stereoisomers of the cyclobutane pyrimidine dimer (Pyr( IPyr). In this study we found that Escherichia coli photolyase binds to the trans-syn-I isomer of T( IT with about 1 04-fold lower affinity than the cis-syn isomer but it repairs it relatively efficiently.