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Molecular and Cellular Biology, July 2007, p. 5014-5028, Vol. 27, No. 13
0270-7306/07/$08.00+0 doi:10.1128/MCB.02339-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Hyuk Wan Ko,1,
,
Wangjie Yu,2
Paul E. Hardin,2 and
Isaac Edery1,3*
Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey 08854,1 Department of Molecular Biology and Biochemistry, Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey 08854,3 Department of Biology and Center for Research on Biological Clocks, Texas A&M University, College Station, Texas 778432
Received 15 December 2006/ Returned for modification 2 February 2007/ Accepted 11 April 2007
A common feature of animal circadian clocks is the progressive phosphorylation of PERIOD (PER) proteins from hypo- to hyperphosphorylated species, events that are highly dependent on casein kinase 1
(termed DOUBLETIME [DBT] in Drosophila melanogaster) and necessary for normal clock progression. Drosophila PER (dPER) functions in the negative limb of the clockworks by presumably binding to the transcription factor CLOCK (CLK) and inhibiting its transactivation activity. Here, we identify a small region on dPER that is conserved with mammalian PERs and contains the major in vivo DBT binding domain, termed dPDBD (for dPER DBT binding domain). This domain is required for the manifestation of molecular and behavioral rhythms in vivo. In the absence of the dPDBD, the dPER protein is present at constant high levels throughout a daily cycle, undergoes little phosphorylation, and is severely impaired in its ability to function as a transcriptional repressor. Our findings indicate that the binding of dPER to CLK is not sufficient for transcriptional inhibition, implicating a more indirect mode of action whereby dPER acts as a molecular bridge to "deliver" DBT and/or other factors that directly repress CLK-dependent gene expression.
Published ahead of print on 23 April 2007.
Equal contributions by E. Y. Kim and H. W. Ko.
Present address: Department of Molecular Biology, Princeton University, Princeton, NJ 08544.
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