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Science 1 May 2009:
Vol. 324. no. 5927, pp. 598 - 599
DOI: 10.1126/science.1174132
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Perspectives

Circadian Rhythms:

A Circadian Loop asSIRTs Itself

Herman Wijnen

Daily time keeping in many organisms depends on internal circadian clocks that temporally organize biological functions relative to each other as well as the environment. These clocks generate rhythms in physiology and behavior by using circuits of gene expression that are organized in negative-feedback loops (1). Two studies in this issue, by Nakahata et al. (2) on page 654 and Ramsey et al. (3) on page 651, propose the addition of a new negative-feedback loop to this circuitry that involves the metabolite nicotinamide adenine dinucleotide (NAD+) and the protein SIRTUIN1 (SIRT1). The new loop suggests connections between the circadian clock and SIRT1-dependent functions associated with cell survival, development, inflammation, and metabolism.

Department of Biology, University of Virginia, Charlottes-ville, VA 22904, USA.

E-mail: hw9u{at}virginai.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)