CIRCADIAN-RHYTHMS IN PROKARYOTES - LUCIFERASE AS A REPORTER OF CIRCADIAN GENE-EXPRESSION IN CYANOBACTERIA

We have used a luciferase reporter gene and continuous automated monit oring of bioluminescence to demonstrate unequivocally that cyanobacter ia exhibit circadian behaviors that are fundamentally the same as circ adian rhythms of eukaryotes. We also show that these rhythms can be st udied by molecular methods in Synechococcus sp. PCC7942, a strain for which genetic transformation is well established. A promoterless segme nt of the Vibrio harveyi luciferase structural genes (luxAB) was intro duced downstream of the promoter for the Synechococcus psbAI gene, whi ch encodes a photosystem II protein. This reporter construction was re combined into the Synechococcus chromosome, and bioluminescence was mo nitored under conditions of constant illumination following entrainmen t to light and dark cycles. The reporter strain, AMC149, expressed a r hythm of bioluminescence which satisfies the criteria of circadian rhy thms: persistence in constant conditions, phase resetting by fight/dar k signals, and temperature compensation of the period. Rhythmic change s in levels of the native psbAI message following light/dark entrainme nt supported the reporter data. The behavior of this prokaryote dispro ves the dogma that circadian mechanisms must be based on eukaryotic ce llular organization. Moreover, the cyanobacterial strain described her e provides an efficient experimental system for molecular analysis of the circadian clock.