FecR is involved in regulation of iron dicitrate transport. In the absence of citrate FecR inactivates FecI. FecR is probably a sensor that recognises iron dicitrate in the periplasm.

1: Novel two-component transmembrane transcription control: regulation of iron dicitrate transport in Escherichia coli K-12. Van Hove B, Staudenmaier H, Braun V; J Bacteriol 1990;172:6749-6758. PMID:2254251