Dual repression by Fe2+-Fur and Mn2+-MntR of the mntH gene, encoding an NRAMP-like Mn2+ transporter in Escherichia coli

The uptake of Mn2+, a cofactor for several enzymes in Escherichia coli, is mediated by MntH, a proton-dependent metal transporter, which also recognizes Fe2+ with lower affinity. NntH belongs to the NRAMP family of eukaryotic Fe2+ and Mn2+ transporters. In E. coli strains with chromosomal mntH-lacZ fusions, mntH was partially repressed by both Mn2+ and Fe2+. inactivation of fur resulted in the loss of Fe2+-dependent repression of mntH transcription, demonstrating that Fe2+ repression depends on the global iron regulator Fur. However, these fur mutants still showed Mn2+-dependent repression of mntH. The Mn2+-responsive transcriptional regulator of mntH was identified as the gene product of o155 (renamed MntR). mntR mutants were impaired in Mn2+ but not Fe2+ repression of mntH transcription. Binding of purified MntR to the mntH operator was manganese dependent. The binding region was localized by DNase I footprinting analysis and covers a nearly perfect palindrome. The Fur binding site, localized within 22 nucleotides of the mntH operator by in vivo operator titration assays, resembles the Fur-box consensus sequence.