Cyanobacteria operate under a circadian clock unlike those found in other organisms. It is driven by periodic phosphorylation of a core clock protein rather than by periodic transcription or translation. Nakajima et al. now show that this oscillator can be reconstituted in vitro with only three clock proteins and a phosphate source, adenosine triphosphate. This supports the notion that biological time measurement in this simple organism is not rooted in the control of gene or protein expression, but in the dynamics of a complex of three proteins in a mechanism that requires little energy.
M. Nakajima, K. Imai, H. Ito, T. Nishiwaki, Y. Murayama, H. Iwasaki, T. Oyama, T. Kondo, Reconstitution of circadian oscillation of cyanobacterial KaiC phosphorylation in vitro. Science 308, 414-415 (2005). [Abstract] [Full Text]