PICOSECOND LASER PHOTOLYSIS STUDIES ON THE PHOTOREPAIR OF PYRIMIDINE DIMERS BY DNA PHOTOLYASE .1. LASER PHOTOLYSIS OF PHOTOLYASE-2-DEOXYURIDINE DINUCLEOTIDE PHOTODIMER COMPLEX

DNA photolyase splits the cyclobutane ring of pyrimidine dimers in DNA in a light-(350-500 nm) driven reaction and thus reverses the harmful effects of far-UV (200-300 nm). The Escherichia coli photolyase contains FADH2 as the catalytic chromophore-cofactor. Using picosecond flash photolysis and the deoxyuridine dinucleotide photodimer, we have obtained the first experimental evidence for a radical intermediate in the reaction, indicating that photorepair is initiated by a photoinduced electron transfer between the pyrimidine dimer and the FADH2 cofactor.