Light-regulated promoters from Synechocystis PCC6803 share a consensus motif involved in photoregulation

A library of Synechocystis PCC6803 (S.6803) DNA cioned in front of the promoterless cat reporter gene of the plasmid pFF11 was used to transform S.6803 to high light-dependent resistance to chloramphenicol. In five clones harbouring a stably replicating pFF11-derived plasmid, this phenotype occurred independently of the photosystem II electron transport and resulted from the correlated increase of CAT activity level and cat mRNA accumulation. The five promoter inserts contained no Escherichia collω70 promoter element, in agreement with their lack of activity in this organism, but shared two conserved motifs. Two secondary mutations, which restored light-regulated promoter activity to an inactive mutant of the smallest insert, mapped within one of the common motifs, emphasizing the probable involvement of this element in photoregulation.