Characterization of two carotenoid gene promoters in the cyanobacterium Synechocystis sp. PCC 6803.

The in vivo promoter activity of the 5'-region of the genes encoding the carotenogenic enzymes phytoene desaturase (crtP) and phytoene synthase (crtB) from the cyanobacterium Synechocystis sp. PCC 6803 has been studied by deletion mapping, primer extension, Northern blot, and using the chloramphenicol acetyltransferase (cat) reporter gene. crtP and crtB are closely linked in the Synechocystis genome, but it is shown that both genes are independently transcribed. The level of transcription in both cases is very low. Their expression is affected in a similar way by light intensity: very little or no expression is observed in the dark compared with expression under illumination conditions. High light intensities induce a transient increase in transcription initiation as detected with the cat probe. DNA fragments containing 81 base pairs upstream of the crtP putative transcription initiation site or 192 base pairs upstream of the crtB putative transcription initiation site are enough to confer light sensitive expression to a reporter gene.