Responses to the major acrolein-derived deoxyguanosine adduct in Escherichia coli

Acrolein, a reactive alpha,beta -unsaturated aldehyde found ubiquitously in the environment and formed endogenously in mammalian cells, reacts with DN A to form an exocyclic DNA adduct, 3H-8-hydroxy-3-(beta -D-2'-deoxyribofura nosyl)-5,6,7,8-tetrahydropyrido[3,2-a]pu rine-9-one (gamma -OH-PdG). The ce llular processing and mutagenic potential of gamma -OH-PdG have been examin ed, using a site-specific approach in which a single adduct is embedded in double-strand plasmid DNA. Analysis of progeny plasmid reveals that this ad duct is excised by nucleotide excision repair. The apparent level of inhibi tion of DNA synthesis is similar to 70% in Escherichia coli Delta recA, uvr A. The block to DNA synthesis can be overcome partially by recA-dependent r ecombination repair. Targeted G --> T transversions were observed at a freq uency of 7 x 10(-4)/translesion synthesis. Inactivation of polB, dinB, and umuD,C genes coding for "SOS" DNA polymerases did not affect significantly the efficiency or fidelity of translesion synthesis. In vitro primer extens ion experiments revealed that the Klenow fragment of polymerase I catalyzes error-prone synthesis, preferentially incorporating dAMP and dGMP opposite gamma -OH-PdG, We conclude from this study that DNA polymerase III catalyz es translesion synthesis across gamma -OH-PdG in an error-free manner. Nucl eotide excision repair, recombination repair, and highly accurate translesi on synthesis combine to protect E. coli from the potential genotoxicity of this DNA adduct.