The Effects of fur on the Transcriptional and Post-transcriptional Regulation of MnSOD Gene (sodA) in Escherichia coli

Earlier studies have shown that the Fur (ferric uptake regulation) protein acts as an anaerobic/aerobic repressor of MnSOD (sodA) expression. We found that the aerobic expression of sodA::lacZ fusion in a Fur− background to be threefold higher than in a Fur+ background. This effect of fur mutation was not seen in a strain harboring the sodA+ gene instead of the sodA::lacZ fusion. However, we observed a proportionate increase in the concentrations of sodA::lacZ and sodA+ mRNAs in response to a mutation in the fur gene. These data suggest that the formation of active MnSOD is dependent on a functional fur gene. Indeed, we found that in a fur mutant iron was incorporated into SodA in place of manganese, thus creating inactive and/or partially active forms of the enzyme (i.e., Fe2SodA and/or Mn,FeSodA, respectively), resulting in little or no increase in total MnSOD activity. Thus, Fur plays the role of a repressor at the transcriptional level, but it also plays an indirect role at the post-transcriptional level where it affects the maturation of SodA into a fully active enzyme, Mn2SodA (MnSOD).