Article
- The EMBO Journal (2007) 26, 4029 - 4037
- doi:10.1038/sj.emboj.7601832
Published online: 23 August 2007
Subject Categories:
A sequential program of dual phosphorylation of KaiC as a basis for circadian rhythm in cyanobacteria
Taeko Nishiwaki1,a, Yoshinori Satomi2,ab, Yohko Kitayama1,a, Kazuki Terauchi1, Reiko Kiyohara1,c, Toshifumi Takao2 and Takao Kondo1
- Division of Biological Science, Graduate School of Science, Nagoya University and SORST, Japan Science and Technology Agency (JST), Furo-cho, Chikusa-ku, Nagoya, Japan
- Institute for Protein Research, Osaka University, Suita-shi, Osaka, Japan
Correspondence to:
Takao Kondo, Division of Biological Science, Graduate School of Science, Nagoya University, and SORST, Japan Science and Technology Agency (JST), Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan. Tel.: +81 52 789 2498; Fax: +81 52 789 2963; E-mail: kondo@bio.nagoya-u.ac.jp
aThese authors contributed equally to this work
bPresent address: Pharmaceutical Research Division, Discovery Research Center, Takeda Pharmaceutical Company Ltd, 17-85 Jusohonmachi 2-chome, Yodogawa-ku, Osaka 532-8686, Japan
cPresent address: Fundamental Tech & Development Div., J-OIL MILLS Inc., Daikoku-cho, Tsurumi-ku, Yokohama-city 230-0053, Japan
Received 29 May 2007; Accepted 23 July 2007
Abstract
The circadian phosphorylation cycle of the cyanobacterial clock protein KaiC has been reconstituted in vitro. The phosphorylation profiles of two phosphorylation sites in KaiC, serine 431 (S431) and threonine 432 (T432), revealed that the phosphorylation cycle contained four steps: (i) T432 phosphorylation; (ii) S431 phosphorylation to generate the double-phosphorylated form of KaiC; (iii) T432 dephosphorylation; and (iv) S431 dephosphorylation. We then examined the effects of mutations introduced at one KaiC phosphorylation site on the intact phosphorylation site. We found that the product of each step in the phosphorylation cycle regulated the reaction in the next step, and that double phosphorylation converted KaiC from an autokinase to an autophosphatase, whereas complete dephosphorylation had the opposite effect. These mechanisms serve as the basis for cyanobacterial circadian rhythm generation. We also found that associations among KaiA, KaiB, and KaiC result from S431 phosphorylation, and these interactions would maintain the amplitude of the rhythm.
Keywords:
- circadian rhythm,
- cyanobacteria,
- in vitro,
- KaiC,
- phosphorylation
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