Cloning and sequencing of a Haemophilus ducreyi fur homolog

Iron regulation in a growing number of bacterial species is being attributed to the presence of a fur (ferric uptake regulation) regulatory system. In the presence of iron, Fur acts as a classical negative regulator, binding conserved sequences within the promoter of iron-repressible genes and blocking transcription. Western blot analysis utilizing Escherichia coli Fur antisera detected a band of approximately 17 kDa in soluble extracts of Haemophilus ducreyi. Additionally, Southern blot hybridization of the H. ducreyi chromosome with a meningococcal fur probe indicated that H. ducreyi might contain a fur homolog. This putative fur homolog was cloned into the E. coli vector pACYC184. This clone was capable of repressing expression of a normally Fur-regulated lacZ fusion in the fur-background of E. coli strain H1780. The deduced amino acid sequence shows H ducreyi fur to be 54% identical and 73% similar to E. coli fur, containing putative DNA-binding and metal-binding domains. These data demonstrate that H ducreyi has a functional fur system.