A homologue of the ‘ferric uptake regulation’ gene () was isolated from the cyanobacterium sp. strain PCC 7942 by an -based repression assay’. The assay uses a reporter-gene construct containing the promoter region of the iron-regulated cyanobacterial gene fused to the coding region for chloramphenicol acetyltransferase. The isolated gene codes for a protein that has 41 % sequence similarity (36% identity) to Fur from and contains the putative iron-binding motif found in the Fur proteins of purple bacteria. No significant similarity was found to the DxtR repressor that regulates the expression of toxin and siderophore production in Gram-positive bacteria. Insertional mutagenesis of the cloned cyanobacterial gene led to the creation of heteroallelic mutants that showed iron-deficiency symptoms in iron-replete medium, including the constitutive production of flavodoxin and of hydroxamate siderophores. Failure to eliminate wild-type copies of the gene from the polyploid genome of 7942 implies that in this cyanobacterium Fur may have essential functions in addition to the regulation of genes involved in iron scavenging or photosynthetic electron transport.


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