Inactivation of the FNR protein of Escherichia coli by targeted mutagenesis in the N-terminal region.

The FNR protein of Escherichia coli is a regulatory protein that activates the transcription of its target genes in response to oxygen limitation. Site-directed mutagenesis was used to show that a 28-residue N-terminal segment containing three cysteines is essential for normal FNR function. The cysteine residue which is centrally located in the three-cysteine cluster (Cys-Ala-Ile-His-Cys-Gln-Asp-Cys) was also shown to be essential for FNR activity. Possible mechanisms by which this cysteine residue might function in the response of FNR to anaerobiosis are discussed.