Abstract
The coordinated high-light response of genes encoding subunits of photosystem I (PSI genes) is achieved by the AT-rich region located just upstream of the core promoter in Synechocystis sp. PCC 6803. The upstream element enhances the basal promoter activity under low-light conditions, whereas this positive regulation is lost immediately after the shift to high-light conditions. We found that a high light regulatory 1 (HLR1) sequence exists in the upstream element of every PSI gene and a response regulator RpaB binds to the HLR1 sequence. In the case of the psaAB genes encoding reaction center subunits, there are two light-responsive promoters and three additional HLR1 sequences, suggesting the complicated mechanism of transcriptional regulation. In this study, we examine the involvement of the HLR1 sequence to the regulation of two promoters in the psaAB genes using reporter constructs with or without mutation in the HLR1 sequences.
