CD measurements were carried out on a Jasco J-810 spectropolarimeter equipped with a programmable temperature-control unit (Julabo HP-4). The concentration of DNA samples were 2 mM. Before the CD spectrum measurement, the DNA samples were annealed by heating to 95uC for 5 min, then rapidly cooled on ice for 10 min, and incubated for another 10 min at room temperature. The spectra from 400 to 200 nm were obtained by using 1 nm slit width and 0.1 nm scanning resolution. Each CD spectrum was an average of 8 scans with the buffer background subtracted.