At the pulse of time: protein interactions determine the pace of circadian clocks

Circadian clocks, internal timekeepers that generate a daily rhythmicity, help organisms to be prepared for periodic environmental changes of light and temperature. These molecular clocks are transcriptional feedback loops that generate 24-h oscillations in the abundance of clock proteins. For the maintenance of this rhythm inside the core clockwork and for its transmission to downstream genes the clock proteins additionally rely on post-transcriptional and post-translational mechanisms. Thus clock proteins engage in a variety of interactions with DNA, RNA and other proteins. Based on the model organisms Drosophila melanogaster and Arahidopsis thaliana molecular principles of eireadian clocks are discussed in this review. (c) 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.