C. difficile LexA regulon genes. (A) SPR sensorgrams of the binding of C. difficile LexA with in silico predicted target DNA sites. Selection of LexA target genes determined by in silico and analysed by SPR. LexA (20 nM) was injected for 60 s across the chip-immobilized DNA fragments containing either of the putative operators and dissociation was followed for 540 s. The representative sensorgrams are shown and the dissociation constants presented as average values of triplicate experiments presented with standard deviation. By n.d. we mark if dissociation rate constant was not determined and the response units are marked by RU. With the MEME tool determined motifs for the target DNA sites found in promoter regions of the genes higher affinity CDR20291_2056, lexA, uvrB, recA, sspB, ruvC, CDR20291_2689, oppC, tcdA, 97b34v1_250108, showing high affinity for LexA (B) or of the genes rplR, rpoB, soj, potC, vanR, CDR20291_2297 to which LexA does not bind stably (C).