Circadian Rhythms

A Clock by Another Mechanism

Science's STKE  18 Jan 2005:
Vol. 2005, Issue 267, pp. tw31
DOI: 10.1126/stke.2672005tw31

The circadian clock enables diverse organisms to adapt their lives to light-dark alterations of the day. It has been thought that a universal clock mechanism that generates and maintains self-sustainable oscillations, or rhythms, is based on a translation-transcription autoregulatory feedback model of core clock elements. Tomita et al. demonstrate that this model does not apply to cyanobacteria, the simplest organism known to show a circadian rhythm. Oscillation in the phosporylation of a core clock protein KaiC persisted in the dark, in the absence of any translation-transcription loop. The basis of the rhythm lies in the autoregulation of phosphorylation by KaiC itself. Thus, the clock model in eukaryotes may not apply to cyanobacteria under certain conditions.

J. Tomita, M. Nakajima, T. Kondo, H. Iwasaki, No transcription-translation feedback in circadian rhythm of KaiC phosphorylation. Science 307, 251-254 (2005). [Abstract] [Full Text]