In Escherichia coli, the iron regulator Fur is regulated by two oxidative-stress response regulators. The generation of dangerous radicals by oxygen and iron is the basis for this dual regulation, which is also found in eukaryotes. The binding of iron-regulated transcripts to apo-aconitase and results of mRNA half-life studies indicate that there is post-transcriptional iron regulation in bacteria, as in eukaryotes. Fur contains two metal-binding sites, one for Zn2+ and one for Fe2+. Zinc uptake systems are regulated by members of the Fur protein family, and zinc is a cofactor. DtxR and related proteins constitute another family of iron regulators, first found in Gram-positive organisms with a high GC content. In organisms with Fur-dependent iron regulation, members of the DtxR family regulate manganese transport.