Exploring the signaling pathway of circadian bioluminescence

Bioluminescence in the unicellular dinoflagellate Gonyaulax polyedra represents an excellent model for studying a circadian controlled process at the biochemical and molecular levels. There are three key components involved in the bioluminescence reaction: the enzyme, luciferase, its substrate, luciferin, and a luciferin-binding protein (LBP), which sequesters the substrate at p^H 7.5 and thus prevents it from reacting with the enzyme. All components are tightly packed together in organdies, designated scintillons. The entire bioluminescent system is under circadian control with maximum amounts in the night. For both proteins circadian control is exerted at the translational level. In case of Ibp mRNA a small interval in its 3'untranslated region serves as a cis -acting element to which a trans -factor binds in a circadian manner. The binding activity of this factor decreases at the beginning of the night phase, when synthesis of LBP starts, and it increases al the end of the night, when synthesis of LBP stops indicating that it functions as a clock-controlled represser.