Editors' ChoiceSystems Biology

Dissecting a Core Oscillator

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Science's STKE  06 Nov 2007:
Vol. 2007, Issue 411, pp. tw407
DOI: 10.1126/stke.4112007tw407

The core circadian oscillator of the cyanobacterium Synechococcus elongatus can be reconstituted in vitro by mixing the proteins KaiA, KaiB, and KaiC, resulting in oscillations in KaiC phosphorylation. The underlying mechanism of this biochemical oscillator has been elusive. Rust et al. (see the Perspective by Poon and Ferrell) now show that phosphorylation of KaiC at two residues is cyclically ordered and that the abundance of each phosphorylated form determines the phase of the oscillator. This sequential phosphorylation of KaiC, combined with negative feedback caused by one of the phosphorylation states, is sufficient to explain stable oscillation.

M. J. Rust, J. S. Markson, W. S. Lane, D. S. Fisher, E. K. O'Shea, Ordered phosphorylation governs oscillation of a three-protein circadian clock. Science 318, 809-812 (2007). [Abstract] [Full Text]

A. C. Poon, J. E. Ferrell Jr., A clock with a flip switch. Science 318, 757-758 (2007). [Summary] [Full Text]