This positive control must be mediated by binding of the S. typhimurium Fur protein to the flhD promoter as indicated by the fact that this promoter tests positive in a Fur titration assay .
This result demonstrates that the Fur protein must bind to the S. typhimurium flhD promoter .
Moreover , the S. typhimurium flhD master operon , is positively regulated by Fur through an iron-independent mechanism .