Demonstration of pyrimidine dimer-DNA glycosylase activity in vivo: Bacteriophage T4-infected Escherichia coli as a model system

An approach to the detection of pyrimidine dimer-DNA glycosylate activity in living cells is presented. Mutants of Escherichia coli defective in uvr functions required for incision of UV-irradiated DNA were infected with phage T4 denV⁺ or denV^- (defective in the T4 pyrimidine dimer-DNA glycosylate activity). In the former case the denV gene product catalyzed the incision of UV-irradiated host DNA, facilitating the subsequent excision of thymine-containing pyrimidine dimers. Isolation of these dimers from the acid-soluble fraction of infected cells was achieved by a multistep thin-layer chromatographic system. Exposure of the dimers to irradiation that monomerizes pyrimidine dimers (direct photoreversal) resulted in the stoichiometric formation of free thymine. Thus, in vivo incision of UV-irradiated DNA dependent on a pyrimidine dimer-DNA glycosylase can be demonstrated.