Zur binding to the regulatory regions of Zur-repressed genes. DNA fragments corresponding to the promoter regions of znuL, znuM, zrpWX and znuK/znuGHI and the coding region of cspD were labeled with 32P and incubated or not with increasing concentrations of purified His-FLAG-Zur (0, 25, 50, 100, 200, 500 and 1000 nM; this latter concentration was used only for cspD). Competition assays were carried out with 0.2 μM of purified His-FLAG-Zur in the presence of 30-fold of unlabeled probe (S) or in the presence of 30-fold of non-specific competitor (N). The non-specific competitor probe was the coding region of the stationary phase-induced gene cspD. Free probe and His-FLAG-Zur bound probe are indicated by (F) and (B), respectively.