Electrophoretic mobility shift assay. The band of DNA fragment containing the promoter region of sycO disappeared with increasing amounts of CRP protein, and a retarded DNA band with decreased mobility turned up (Fig. 3a), which presumably represented the CRP-DNA complex. But for YPO0180 and YPO1099, the CRP-DNA complex did not appear even His-CRP was increased to 4 μg for each reaction mixture (Fig. 3b).