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. 2011 May 19;286(28):25317–25330. doi: 10.1074/jbc.M111.222745

FIGURE 2.

FIGURE 2.

Iron-dependent regulation of fet in a Fur titration assay. E. coli cells containing a fhuF-lacZ fusion and the vector plasmid pGEM®-T-Easy with the fetM promoter (1, 2, and 3; three independent clones), the positive control fhuFp, or no insert (negative control) were cultivated overnight on MacConkey lactose agar plates supplemented with 30 μm Fe(NH4)2(SO4)2 at 37 °C. The presence of a Fur box on a high copy number plasmid titrates the Fur repressor away from fhuF-lacZ and leads to β-galactosidase activity. This results in lactose consumption and purple staining of the colonies.