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Access through your institution Buy or subscribe Chang _et al_. used NMR spectroscopy and gel filtration to investigate the binding of _Thermosynechococcus elongatus_ KaiB to hexameric
S431E-KaiC, a phosphomimic of serine-phosphorylated KaiC, and also to hexameric complexes of isolated CI and S431E-CII domains. Whereas KaiB could bind S431E-KaiC, the authors observed no
binding of KaiB to the isolated CI or S431E-CII rings individually, but binding was restored when the two domains were added together. When a FLAG epitope was added to the CI domain to
weaken the interaction with CII, KaiB could not bind, suggesting that stacking of the hexameric rings formed by the KaiC CI and CII domains is important for the formation of the KaiB–KaiC
complex. Previous work had suggested that, in _Synechococcus elongatus_, KaiB interacts with the CII domain of KaiC. However, the authors found that, in _T. elongatus_ at least, KaiB bound
to the CI and not the CII domain, but only when CI had been dissociated from a hexameric ring to form monomers by increasing the ADP/ATP ratio in the solution. This suggests that the
KaiB-binding site is normally hidden in the hexameric CI ring. Binding of KaiB to the KaiA–KaiC complex is thought to lead to the sequestration of KaiA at the CI domain, thereby terminating
the phosphorylation phase of the oscillation cycle and promoting dephosphorylation. Accordingly, the authors found that addition of KaiA to a solution containing monomeric CI and KaiB led to
the formation of a complex containing all three proteins. This is a preview of subscription content, access via your institution ACCESS OPTIONS Access through your institution Subscribe to
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support REFERENCES ORIGINAL RESEARCH PAPER * Chang, Y. et al. Rhythmic ring-ring stacking drives the circadian oscillator clockwise. _Proc. Natl Acad. Sci. USA_ 11 Sep 2012
(doi:10.1073/pnas.1211508109) Article CAS Google Scholar FURTHER READING * Lenz, P. & Søgaard-Andersen, L. Temporal and spatial oscillations in bacteria. _Nature Rev. Microbiol._ 9,
565–577 (2011) Article CAS Google Scholar Download references Authors * Andrew Jermy View author publications You can also search for this author inPubMed Google Scholar RIGHTS AND
PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Jermy, A. Uncovering the circadian clockwork. _Nat Rev Microbiol_ 10, 730 (2012).
https://doi.org/10.1038/nrmicro2896 Download citation * Published: 08 October 2012 * Issue Date: November 2012 * DOI: https://doi.org/10.1038/nrmicro2896 SHARE THIS ARTICLE Anyone you share
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