| Three psbA genes encoding the D1 protein of the photosystem II reaction center are differentially expressed under different light intensities in the cyanobacterium Synechococcus sp. strain PCC 7942. When light intensity is increased from 125 ;Soluble proteins from Synechococcus enriched for DNA-binding activity was demonstrated to specifically bind to the psbAII enhancer and high-light-responsive DNA sequences downstream of the transcription start site. In vivo, protein binding to the upstream region of psbAII was observed only in high-light exposed cell samples but not in those maintained at low light. When 12 bp from the psbAII protein binding sites were deleted, protein binding was impaired and high-light induction of both transcriptional and translational lacZ reporters was significantly reduced, indicating that the protein binding to this region is required for high-light-induced psbAII gene expression. The mutant element also showed impaired enhancer activity when combined with the heterologous E. coli conII promoter. |
