Repair of DNA double-strand breaks in UV-irradiated Escherichia coli uvrB recF cells is inhibited by rich growth medium.

Ultraviolet (UV)-irradiated uvrB recF and uvrB recB cells of Escherichia coli K-12 showed similar radiation sensitivities when plated on minimal growth medium (MM), however, the uvrB recF cells were much more UV radiation-sensitive than the uvrB recB cells when plated on rich growth medium. Sedimentation analysis of the DNA from UV-irradiated uvrB recF cells suggests that the rich medium killing of uvrB recF cells is due to the inhibition of the repair of UV-radiation-induced DNA double-strand breaks, i.e., the killing is due to the inhibition of the recB-dependent pathway of postreplication repair. Furthermore, we demonstrated that the DNA double-strand breaks that were formed in UV-irradiated uvrB recA200(Ts) cells incubated at 42 degrees C in rich growth medium were not repaired whether the medium during subsequent repair incubation at 30 degrees C was MM or rich growth medium, while DNA double-strand breaks that were formed in MM at 42 degrees C could be repaired in MM or in rich growth medium at 30 degrees C. How the absence of an abrupt slowing of DNA synthesis when UV-irradiated cells are held in rich growth medium (Sharma and Smith, 1985b) may prevent the repair of these DNA double-strand breaks is discussed.