FIG 4.

Fur binds to the 4532 promoter and prevents access to RNA polymerase in vitro. (A) Electrophoretic mobility shift assay of the EC042_4532 promoter (P₄₅₃₂) with the indicated concentration of Fur in the presence of FeCl₃ or in the presence of EDTA or using a purified NtrC transcriptional activator. Controls include Fur shift assays of the Fur-dependent sci1 promoter or of the Fur-independent sci2 promoter. DNA-Fur complexes are indicated by stars. (B) Densitometry analysis of Fur binding on the P₄₅₃₂ fragment, represented as free P₄₅₃₂ DNA as a function of Fur concentration. (C) Electrophoretic mobility shift assay of the unmethylated (P₄₅₃₂) or methylated (me-P₄₅₃₂) EC042_4532 promoter with the indicated concentration of σ⁷⁰-RNAP alone or in the presence of 20 nM Fur. DNA-Fur and DNA-RNAP complexes are indicated by the star and circle, respectively. (D) Densitometry analysis of RNAP binding on the unmethylated (blue curve), methylated (green curve), or Fur-bound unmethylated (red curve) P₄₅₃₂ fragment, represented as RNAP-bound DNA as a function of RNAP concentration.