The SOS response is a cascade of consecutive reactions induced by cell DNA damage. The genes directly involved in these reactions are regulated by LexA, which binds to specific nucleotide sequences in their upstream regions. The presence of such a sequence in the regulatory gene region can be used as a criterion to identify the genes potentially involved in the SOS response. A study was made of the genes whose regulation is specific to particular taxa (Enterobacteriales, Pasteurellales, Vibrionales, Pseudomonadales, and Alteromonadales). Some of the genes identified have not been implicated in the SOS response as yet but have a conserved LexA-binding site in the regulatory region and perform a function probably associated with the cell response to DNA damage. These genes include mfd, whose product facilitates DNA repair when transcription is arrested because of DNA damage; VC0082, coding for recombinase; and VP2449, which is responsible for xenobiotic resistance. The composition and evolution of the LexA regulon in γ-proteobacteria are considered.