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. 2024 Oct 23;15(11):e02310-24. doi: 10.1128/mbio.02310-24

Fig 8.

Illustration of iron regulation in wild-type and Δfpa mutant strains. In iron-starved conditions, Fur activates transcription in wildtype, while iron-replete conditions inhibit it. In Δfpa mutant, transcription is inhibited regardless of iron levels.

Working model for Fpa function. In our model, Fur (gray) and Fpa (cyan) bind Fe(II) transiently. They are both metalated in Fe-replete growth conditions, and Fur directly prevents transcription of genes coding for Fe acquisition machinery via binding to a consensus sequence of DNA in the operator termed a Fur box. Upon Fe limitation, Fpa forms a complex with Fur preventing Fur from binding to Fur box DNA, thus alleviating Fur repression of target genes. The oligomeric state of the heterocomplex is currently unknown.