Circular dichroism (CD) spectra were obtained using a JASCO-815 CD spectropolarimeter. Temperature was controlled by circulating water at the desired temperature in the cell jacket. TcaR and DNA samples were prepared under the conditions identical to those prepared for EMSA assay. The CD spectra were collected between 250 and 200 nm with 1 nm bandwidth at 1 nm intervals. All spectra were obtained from an average of five scans. The photomultiplier absorbance did not exceed 600 V during the analysis. CD spectra were normalized by subtraction of the background scan with buffer alone. The mean residue ellipticity, [h], was calculated based on the equation, [h] = MRW6hl/ 106l6c, where MRW is the mean residue weight, hl is the measured ellipticity in milidegrees at wavelength l, l is the cuvette pathlength (0.1 cm), and c is the protein concentration in g/mL.