The X-ray induction of SOS repair activity in E. coli: euoxic vs. anoxic DNA damage

The induction of DNA repair (the "SOS Response") by X rays has been studied in E. coli GE94, irradiated under euoxic versus anoxic conditions. GE94 contains a recA-lacZ gene fusion that allows the radiation-induced transcription of recA to be followed by measuring the changes in beta-galactosidase levels. At doses up to about 450 Gray, more recA transcription (indicating more DNA damage capable of inducing SOS repair activity) occurs in cells irradiated in air instead of 100% nitrogen. Although the presence of dissolved oxygen cannot change the initial number of DNA radicals (initial "energy-deposition events"), apparently more of these radicals become stable lesions when oxygen is present.