Response of recA-dependent operons to different DNA damage signals

The responses of three recA-dependent operons (recA, lambda, and phi 80), with three different repressors, to five DNA damage treatments were compared. Each operon shows a unique induction onset time constant over a wide dose range. However, the extent of response is variable within the same dose range. Individual Escherichia coli cells show a graded SOS response to different levels of DNA damage. Apparently phage repressors have evolved to discriminate between lethal and sublethal DNA damage to a host by a wide variety of agents. Multiple induction signals could account for the complex behavior of this system. For example, the absence of the recBC enzyme from a cell leads to complex changes in SOS induction onset times and extents.