PHOTOSYNTHETIC ELECTRON-TRANSPORT CONTROLS DEGRADATION BUT NOT PRODUCTION OF PSBA TRANSCRIPTS IN THE CYANOBACTERIUM SYNECHOCYSTIS-6803

Accumulation and stability of psbA and rbcL-S transcripts in Synechocystis 6803 was followed in the presence and absence of the photosynthesis inhibitors DCMU and methylviologen. Our results demonstrate that both transcript production and transcript stability are important regulatory elements for psbA gene expression in Synechocystis 6803. The production of psbA transcripts was stimulated by light in a process that operated independently of the photosynthetic electron transport. However, stability of the psbA transcript increased in the dark and was controlled by photosynthetic electron transport. The psbA transcript was remarkably stable in the dark, with a half-life of approximately 7 hours. By contrast, the regulatory pattern for the rbcL-S genes was quite different. The light-stimulated production of rbcL-S transcripts was dependent on an intact photosynthetic electron transport, and rbcL-S transcript stability was higher under illuminated conditions than in darkness.