The function of the gene encoding the ferritin from was investigated using the Fur titration assay (FURTA) in and by characterization of a -deficient mutant strain of Nucleotide sequence analysis revealed that the region is conserved among strains (>95% nucleotide identity). Two transcriptional start sites, at least one of them preceded by a s-dependent promoter, were identified. Provision of the gene on a multicopy plasmid resulted in reversal of the Fur-mediated repression of the gene in thus enabling the use of the FURTA for cloning of the ferritin gene. Inactivation of the gene, either by insertion of a resistance cassette or by deletion of the up- and downstream segments, abolished this function. Immunoblot analysis with a Pfr-specific antiserum detected the Pfr protein in and in carrying the gene on a plasmid. Pfr-deficient mutants of were generated by marker-exchange mutagenesis. These were more susceptible than the parental strain to killing by various metal ions including iron, copper and manganese, whereas conditions of oxidative stress or iron deprivation were not discriminative. Analysis by element-specific electron microscopy revealed that growth of in the presence of iron induces the formation of two kinds of cytoplasmic aggregates: large vacuole-like bodies and smaller granules containing iron in association with oxygen or phosphorus. Neither of these structures was detected in the -deficient mutant strain. Furthermore, the ferritin accumulated under iron overload and the -deficient mutant strains lacked expression of a 12 kDa protein which was negatively regulated by iron in the parental strain. The results indicate that the nonhaem-iron ferritin is involved in the formation of iron-containing subcellular structures and contributes to metal resistance of Further evidence for an interaction of ferritin with iron-dependent regulation mechanisms is provided.


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