Expression of the iron-responsive irpA gene from the cyanobacterium Synechococcus sp. strain PCC 7942

Expression of the iron-stress-induced irpA gene of Synechococcus sp. strain PCC 7942 was investigated by constructing luminescent pirpA::luxAB promoter fusions. Growth of Fe-replete and Fe-limited cultures yielded high levels of luminescence only under conditions of iron deficiency. Promoter fusion deletions revealed that low Fe irpA transcription is dependent on a 25-nucleotide sequence that includes a region of dyad symmetry centered 19 nucleotides from the transcription start. Assaying luminescence at defined iron concentrations in trace-metal-buffered media showed that irpA transcription is activated at concentrations below 100 nm Fe. Overall, the expression pattern and promoter structure of irpA suggests a novel form of metal-dependent regulation in this species