FIGURE 6.

Fur competes with LuxO for binding to regions upstream of qrr genes. A, electrophoresis mobility shift assay of binding competition between LuxO and Fur for qrr promoter regions. Ten ng of each qrr promoter was incubated with either LuxO, Fur, or both. Lanes 1–6 include each probe incubated with the following: lane 1, no protein; lane 2, 1 μm Fur; lane 3, 2 μm Fur; lane 4, 800 nm LuxO; lane 5, 800 nm LuxO with 1 μm Fur; lane 6, 800 nm LuxO with 2 μm Fur. Positions of probes bound and shifted by LuxO or Fur are indicated by arrows. This result is representative of two independent experiments. B, DNase I footprinting of Fur protein binding to each qrr. A ³²P-labeled probe (200 ng) was incubated with increasing concentrations of Fur (0, 250 and 500 nm, and 1 μm). The nucleotide sequences protected by Fur (shaded boxes), the σ⁵⁴-binding site (unshaded boxes), and the consensus LuxO-binding sites (hatched boxes) are indicated.