Biologjia Online

A Clock by Another Mechanism

Science, Vol 307, 14 January, 2005

The circadian clock enables diverse organisms to adapt their life 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. (p. 251) 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.

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