A photosystem 1 psaFJ-null mutant of the cyanobacterium Synechocystis PCC 6803 expresses the isiAB operon under iron replete conditions

A psaFJ-null mutant of Synechocystis sp. strain PCC 6803 was characterised. As opposed to similar mutants in chloroplasts of green algae, electron transfer from plastocyanin to photosystem 1 was not affected. Instead, a restraint in full chain photosynthetic electron transfer was correlated to malfunction of photosystem 1 at its stromal side. Our hypothesis is that absence of PsaF causes oxidative stress, which triggers the induction of the 'iron stress inducible' operon isiAB. Products are the IsiA chlorophyll-binding protein (CP43') and the isiB gene product flavodoxin. Supporting evidence was obtained by similar isiAB induction in wild type cells artificially exposed to oxidative stress. (C) 2003 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.