Fur proteins are global regulators present in all prokaryotes. In Anabaena sp. PCC 7120 FurA controls iron uptake and modulates an important set of genes related primarily to photosynthesis, nitrogen metabolism and oxidative stress defense. Expression of furA is tuned by the cis-acting antisense α-furA RNA that is co-transcribed with the outer-membrane protein Alr1690. Disruption of the α-furA-alr1690 message produces the iron-deficient JAH3 mutant that lacks Alr1690 and shows enhanced expression of FurA. JAH3 cells present severe structural disorders related to the number, organization and density of photosynthetic membranes. Quantitative analysis of the fluorescence induction shows that the mutation affects the J–I and I–P phases and causes important alterations in the photosynthetic apparatus, leading to lower photosynthetic performance indexes. These results reveal that expression of the α-furA-alr1690 message is required for maintenance of a proper thylakoid arrangement, efficient regulation of iron uptake and optimal yield of the photosynthetic machinery.

This work was founded by the Spanish Ministerio de Educación y Ciencia(BFU2006-03454). Support by Swiss National Foundation to RJS is acknowledged (Nr200021-116765).

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