SufS is a NifS-like protein, and SufD is necessary for stability of the [2Fe-2S] FhuF protein in Escherichia coli

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 w ere shown to be regulated by the iron-dependent Fur repressor. Sequence ana lysis revealed that the sufS open reading frame corresponds to orf f406. Th e protein SufS belongs to the family of NifS-like proteins, which supply su lfur for [Fe-S] centers. The protein FhuF contains a [2Fe-2S] center. A mut ation in the upstream sufD gene (orf f423) caused the same phenotype. The T 7 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 pr otein in a Delta sufD strain failed. Radioactive labeling of N-His-FhuF wit h [S-35]methionine showed that the protein was unstable in the Delta sufD m utant.