FIG. 5.

DNase I footprints of the ArsR protein bound to the arsBHC promoter-operator region. (A) DNA fragments of the arsBHC promoter-operator region were labeled at positions −132 (coding strand) and +105 (noncoding strand) and subjected to DNase I footprint analysis using increasing quantities of purified ArsR protein (0.025, 0.063, 0.126, and 0.252 μg), as described in Materials and Methods. The regions of the DNA protected by ArsR are indicated by bars. (B) Alignment of ArsR DNA binding sites in the E. coli plasmid R773-encoded and chromosomal (chr) ars operons and in the Synechocystis arsBHC operon. The DNA sequence that was protected in DNase I footprinting experiments is shown in the case of the E. coli ars operons. The Synechocystis sequence corresponds to one of the two identical direct repeats found in the ArsR-protected region (Fig. 3B). The numbers indicate the position of the sequence with respect to the transcription start point.