Fig 3. Fluorescence quenching.

The excitation and emission of tryptophan fluorescence were detected at 295 and 340 nm, respectively. The protein solution (0.1 μM; tetramer) in 2 mL Tris—HCl buffer (20 mM Tris—HCl, and pH 8.0) containing 200 or 500 mM NaCl was titrated with increasing quantities of dT65 oligonucleotide. After the addition of ssDNA, the complex solution was equilibrated for 300 s until no fluorescence change could be observed.