The formation of photoreactivable damage by direct excitation of DNA in X-irradiated E. coli cells.

The role of the direct excitation process in the formation of photoreactivable damage (pyrimidine dimers) in E. coli WP2 hcr-exr- cells has been studied. The pyrimidine dimers were detected by photoreactivation following anoxic irradiation by X-rays (220 kVp). The dose modifying factor (DMF) is 1.28 +/- 0.09. A biophysical model is used for a theoretical examination of the importance of the direct excitation process in the formation of photoreactivable damage and the experimental data are consistent with this model.