FIG. 4.
Boundaries of the PurR DNA binding site. The top line represents the wild-type sequence of the B. subtilis pur operon from −177 to +24 relative to the transcription start site (from Fig. 2). PurBox1 (−81 to −68) is red, PurBox2 (−51 to −38) is yellow, and other wild-type regions are black. Nonspecific plasmid DNA generated by using alternative restriction sites is shown in blue. The stated nucleotide range is the position of the wild-type sequence relative to the transcription start site for each construct. The stated length is the total length, including any nonspecific DNA. Apparent Kd values for each fragment were determined by gel retardation assay. The actual DNA length is 1 to 2 unpaired nucleotides longer due to restriction digestion.