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Escherichia coli fhuF mutants, a sufS::MudI mutant, and a sufD::MudI mutant were found to have the same phenotype: the inability to use ferrioxamine B as an iron source in a plate assay. In addition, the sufS and sufD genes were shown to be regulated by the iron-dependent Fur repressor. Sequence analysis revealed that the sufS open reading frame corresponds to orf f406. The protein SufS belongs to the family of NifS-like proteins, which supply sulfur for Fe-S centers. The protein FhuF contains a 2Fe-2S center. A mutation in the upstream sufD gene (orf f423) caused the same phenotype. The T7 expression system and a His tag allow the isolation in good yield of the FhuF protein from a wild-type strain. In contrast, overproduction of the protein in a DeltasufD strain failed. Radioactive labeling of N-His-FhuF with 35Smethionine showed that the protein was unstable in the DeltasufD mutant.
Patzer et al. (1999) studied this question.