The evolution of the cyanobacterial protein clock from a simple light-driven timer

The evolution of the cyanobacterial circadian clock may have progressed through three distinct stages: from a masking mechanism to an hourglass, and finally to a functional clock.

• Cyanobacteria are among the earliest organisms on Earth.
• Recent studies have clarified the molecular components of cyanobacterial circadian clocks.
• The three key clock proteins in cyanobacteria are KaiA, KaiB, and KaiC.
• A scenario has been proposed outlining a gradual evolution of the circadian clock in cyanobacteria.

Simplified