TABLE 4.

Promoter activities of IRP6 in the presence or absence of DtxR in an E. coli system^a

Plasmid	Iron level	β-Galactosidase activity (Miller units)
		− dtxR	+ dtxR
pQF50	Low	0.9 ± 0.2	1.2 ± 0.3
	High	0.7 ± 0.1	1.0 ± 0.2
pQF6	Low	87.7 ± 9.1	78.8 ± 8.6
	High	83.0 ± 0.3	1.4 ± 0.2
pQF6-	Low	1.4 ± 0.3	1.6 ± 0.6
	High	1.2 ± 0.3	0.9 ± 0.0
pQF1	Low	84.7 ± 8.7	6.8 ± 2.4
	High	69.7 ± 6.4	0.8 ± 0.2
pQF1-	Low	0.5 ± 0.1	0.8 ± 0.2
	High	0.5 ± 0.0	0.5 ± 0.2

^aCells were grown in LB medium treated with Chelex-100 resin, and overnight cultures were used for β-galactosidase activity assays. Low iron, addition of 200 μg of EDDA/ml; high iron, addition of 10 μM FeCl₃. Values represent the means ± standard deviations of assays performed on cultures grown in triplicate. −dtxR, without a plasmid that carries dtxR; +dtxR, with a plasmid that carries dtxR.