Abstract
In Synechocystis sp. PCC 6803, promoter activities of photosystem (PS) I genes decrease under high-light and increase under low-light conditions. To know the mechanism of the coordinated regulation of PSI genes, we investigated promoter architectures of psaAB genes encoding reaction center subunits and psaD gene encoding a small subunit of PS I. It was revealed that both psaAB and psaD genes have two promoters (P1 and P2). Although both promoters in psaAB showed light response, the regulatory mechanism was different between them: P1 was activated specifically under low-light conditions, whereas P2 activity was repressed under high light. As for psaD gene, activity of P1 was very weak and did not decrease under high light. P2 showed light response and its activity was up-regulated under low-light conditions. Although the regulatory mechanism seems similar between P1 of psaAB and P2 of psaD, we could not find common cis-elements for these two promoters.
