Activation of FNR-dependent transcription by iron: An in vitro switch for FNR

FNR is an iron-binding transcriptional regulator of Escherichia coli which controls the expression of target genes in response to anaerobiosis. The mechanism used by FNR to sense and respond to anaerobiosis is unknown but it is thought to involve iron. In vitro transcription analyses have shown that iron-deficient FNR is unable to activate transcription from the FF-melR promoter, but activity could be restored by preincubation with Fe²⁺ and β-mercaptoethanol. The reactivation of FNR was prevented and reversed by chelating agents, and this reactivation thus provides an artificial in vitro switch for FNR-dependent transcriptional activation.