Specific DNA precludes C. difficile RecA*-LexA interaction. Interaction of C. difficile LexA repressor (2.6 μM) incubated with specific, 22-bp recA operator (A) or with non-specific DNA fragment, recA operator with modified six nucleotides (B), with the chip-immobilized C. difficile RecA* (~2000 response units). The used DNA interacting with repressor was in 1.4 μM (black line), 2.7 μM (red line), 4.0 μM (green line), 5.4 μM (blue line), 8.1 μM (pink line) concentration. The cyan line presents sensorgram of the free DNA at 8.1 μM concentration interacting with the RecA*. (C) In vitro repressor cleavage pattern exhibits that purified E. coli and C. difficile key SOS players can cross-react. C. difficile proteins are marked as RecA* (CD), LexA (CD) and E. coli proteins as RecA* (EC) and LexA (EC), respectively. Time course (min) of either C. difficile or E. coli RecA*-induced inactivation of LexA (CD) or LexA (EC) repressor. Quantification of LexA is presented on the gel above the respective band as the ratio (%) of the protein density value of the initial sample (0 min) relative to the density value obtained from the proteins after indicated time points after addition of RecA*, shown with standard deviation.