Characterization of a stress-responsive operon in the cyanobacterium Synechocystis sp. strain PCC 6803

We previously identified a gene, slr0374, in the unicellular cyanobacterium, Synechocystis sp. strain PCC 6803, that was highly expressed under iron-deficient conditions [J. Bacteriol. 182 (2000) 3536]. The gene product contains an AAA domain, a putative leucine zipper and a phosphorylation site and is part of an operon (with slr0373 and slr0376) that is responsive to various environmental stresses. Primer extension mapping and transcript analysis in insertion mutants showed that all transcripts from this operon originated upstream of slr0373 at four contiguous transcription start sites before being processed into individual transcripts. Both primary and processed transcripts were quite stable. The start sites were sensitive to changes in sulfur, light and redox agent, as well as iron. The structural and regulatory elements of this operon were highly conserved in phycobilisome-containing cyanobacteria that have been sequenced to date. Slr0374 and Slr0376 show homology with Ycf46 and Ycf35, respectively.