Upstream of the SOS response: figure out the trigger.

The bacterial SOS regulon encodes a response to DNA damage that not only functions to relieve the incurred damage but also enhances adaptation through mutagenesis and the lateral spread of virulence factors. Recent papers have demonstrated that certain stimuli can indirectly generate the SOS-inducing signal by activation of endogenous DNA damage mechanisms rather than by direct DNA damage. We suggest that these endogenous triggers have been recruited by bacteria to enable adaptation to various types of stresses.