Figure 5.

CsoR^Sl binding to csoR-EXT enhances A-DNA traits. Insert, the CD spectrum of csoR-EXT (black) in aqueous solution at pH 7.5 reveals a positive ellipticity at 263.5 nm consistent with A-DNA characteristics ascribed to its G-tract palindromes and retains the same ellipticity in the 260 nm region on induction of true A-DNA form in 80% TFE (purple). No signals from CsoR^Sl contribute in the near-UV CD spectrum (black dashed), whereas the ellipticity of csoR-EXT (10 µM) in the near-UV region changes in the presence of one (40 µM) and two molar equivalents (80 µM) of CsoR^Sl (blue) with no further change in the presence of three molar equivalents (120 µM) of CsoR^Sl (green). At two molar equivalents of Cu(I)-CsoR (grey), the near-UV CD spectrum of csoR-EXT is the same as in the absence of the apo-CsoR^Sl. All curves of protein–DNA complexes were baselined with appropriate concentrations of protein and buffer.