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FEBS Lett. 2005 Apr 25;579(11):2289-93.

The chlorophyll-binding protein IsiA is inducible by high light and protects the cyanobacterium Synechocystis PCC6803 from photooxidative stress.

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CEA/Cadarache, DSV, DEVM, Laboratoire d'Ecophysiologie de la Photosynth├Ęse, UMR 6191 CNRS-CEA-Aix Marseille II, Saint-Paul-lez-Durance, France.


The products of the isiAB operon are a chlorophyll antenna protein (IsiA) and flavodoxin (IsiB), which accumulate in cyanobacteria grown under iron starvation conditions. Here we show that strong light triggers de-repression of isiAB transcription and leads to IsiA and flavodoxin accumulation under iron replete conditions. Genetic deletion of isiAB resulted in a photosensitive phenotype, with accumulation of reactive oxygen species and cell bleaching in high light, while the flavodoxin-deficient isiB null mutant expressing isiA was phototolerant. We conclude that IsiA protects cyanobacteria from photooxidative stress. IsiA is the first example of a chlorophyll antenna protein outside the extended LHC family that is induced transiently by high light and that fulfills a photoprotective role.

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