(A) The secondary structure of WT Mtb LexA, LexAΔ24aa, LexAΔ18aa, and LexA RKG/AAA were compared using CD spectroscopy, monitored at wavelengths ranging from 195 to 280 nm. (B) Gel image showing glutaraldehyde cross-linking of Mtb LexA and its variants. Dimeric states of proteins are boxed. (C-F) Changes in extrinsic fluorescence spectra of the proteins, (C) WT Mtb LexA, (D) LexA RKG/AAA, (E) LexAΔ18aa and (F) LexAΔ24aa, as seen when incubated at 1:2 ratios with non-biotinylated dnaE2 ‘SOS’ box (sequence given in Table 1) indicates the conformational changes of the proteins upon DNA binding. Fluorescence intensity is shown in arbitrary units.