FIG. 6.

Substitution analysis of the cysD promoter region. Upper panel: sequence of cysD wild-type and mutated promoter region. Position +1 corresponds to the experimental transcriptional start. The deduced −10 and −35 boxes are underlined, and the putative FhuR DNA-binding box 1 is shaded. Shifts + and − indicate the observation of a band shift or not, respectively, of the corresponding DNA fragment in the presence of the purified FhuR protein. Letters A to F on the right refer to the corresponding lower panel. Lower panel: gel mobility shift assay corresponding to the cysD promoter region as indicated in the upper panel. The experimental procedures are the same as those presented for Fig. 5. (A) cysD wild-type promoter region. (B to F) Mutated sequences indicated on the right column of the upper panel. In each binding assay, the bands for the probe (free) and the FhuR-probe complex (bound) are indicated by an arrow and an arrow with an asterisk, respectively.