LIGHT-REGULATED PROMOTERS FROM SYNECHOCYSTIS PCC6803 SHARE A CONSENSUS MOTIF INVOLVED IN PHOTOREGULATION

A library of Synechocystis PCC6803 (S.6803) DNA cloned in front of the promoterless cat reporter gene of the plasmid pFF11 was used to trans form S.6803 to high light-dependent resistance to chloramphenicol. In five clones harbouring a stably replicating pFF11-derived plasmid, thi s phenotype occurred independently of the photosystem II electron tran sport and resulted from the correlated increase of CAT activity level and cat mRNA accumulation. The five promoter inserts contained no Esch erichia coli sigma(70) promoter element, in agreement with their lack of activity in this organism, but shared two conserved motifs. Two sec ondary mutations, which restored light-regulated promoter activity to an inactive mutant of the smallest insert, mapped within one of the co mmon motifs, emphasizing the probable involvement of this element in p hotoregulation.