Escherichia coli DNA photolyase stimulates uvrABC excision nuclease in vitro.

Pyrimidine dimers are the major photoproducts produced in cellular DNA upon UV irradiation. In Escherichia coli there are dark and photorepair mechanisms that eliminate the dimers from DNA and prevent their lethal and mutagenic effects. To determine whether these repair mechanisms act cooperatively or competitively in repairing DNA, we investigated the effects upon one another of DNA photolyase, which mediates photorepair, and uvrABC excision nuclease, an enzyme complex of the uvrABC gene products, which catalyzes nucleotide excision repair. We found that photolyase stimulates the removal of pyrimidine dimers but not other DNA adducts by uvrABC excision nuclease. The two subunits of uvrABC excision nuclease, the uvrA and uvrB proteins which together bind to the dimer region of DNA, had no effect on the activity of photolyase. T4 endonuclease V, which like photolyase is specific for pyrimidine dimers, was inhibited by photolyase, suggesting that these two proteins recognize the same or similar chemical structures in UV-irradiated DNA that are different from those recognized by uvrABC excision nuclease.