The cyanobacterial circadian clock is based on the intrinsic ATPase activity of KaiC
C. Robertson McClung *
Department of Biological Sciences, Dartmouth College, Hanover, NH 03755
The earth rotates on its axis with a period of 24 h, imposing a dramatic diurnal oscillation on the biosphere. Endogenous biological clocks with circadian periods of ≈24 h are nearly ubiquitous, from bacteria to humans, and serve to coordinate organisms with these daily environmental changes. These clocks make important contributions to fitness, and, in competitive environments, disruption of the circadian clock has dire consequences in cyanobacteria, plants, and mammals (1). Enormous progress has been made in elucidating the mechanism of circadian timekeeping in the cyanobacterium Synechococcus elongatus PCC 7942. The kaiABC locus is essential for rhythmicity (2), and recently a self-sustaining and temperature-compensated circadian rhythm in the phosphorylation of KaiC has been reconstituted in vitro in a minimal system containing the three Kai (Japanese for “cycle”) proteins plus ATP (3, 4). In a recent issue of PNAS, Terauchi et al. (5) established that the ATPase activity of KaiC is the fundamental reaction underlying the cyanobacterial circadian oscillation (Fig. 1).
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