FIGURE 4.

DNase I footprinting of the irr promoter with B. japonicum Fur and Irr. A, protection of DNA from DNase I digestion by Fur or Irr was carried out in the presence of MnCl₂ and 0, 5, 10, 25, or 50 nm Fur or 0, 25, 150, 250, or 500 nm Irr. DNA was radiolabeled with ³²P at the 5′-end of the non-template strand, and thus, the 3′-end is at the top of the gel. Brackets represent the protected regions of Fur and Irr. The open arrowhead indicates a DNase I-hypersensitive site caused by Fur binding. The closed arrowheads represent the DNase I-hypersensitive sites caused by Irr binding. B, the sequence of the irr promoter region protected by Irr or Fur is shown. The bent arrow represents the transcriptional start site of irr. The arrows over the sequence show the three imperfect direct repeat sequences shown previously to be necessary for Fur binding.