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Science 15 April 2005:
Vol. 308. no. 5720, pp. 414 - 415
DOI: 10.1126/science.1108451
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Reports

Reconstitution of Circadian Oscillation of Cyanobacterial KaiC Phosphorylation in Vitro

Masato Nakajima, Keiko Imai, Hiroshi Ito, Taeko Nishiwaki, Yoriko Murayama, Hideo Iwasaki, Tokitaka Oyama, Takao Kondo*

Kai proteins globally regulate circadian gene expression of cyanobacteria. The KaiC phosphorylation cycle, which persists even without transcription or translation, is assumed to be a basic timing process of the circadian clock. We have reconstituted the self-sustainable oscillation of KaiC phosphorylation in vitro by incubating KaiC with KaiA, KaiB, and adenosine triphosphate. The period of the in vitro oscillation was stable despite temperature change (temperature compensation), and the circadian periods observed in vivo in KaiC mutant strains were consistent with those measured in vitro. The enigma of the circadian clock can now be studied in vitro by examining the interactions between three Kai proteins.

Division of Biological Science, Graduate School of Science, Nagoya University, and the Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Agency (JST), Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.

* To whom correspondence should be addressed. E-mail: kondo{at}bio.nagoya-u.ac.jp

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