Title:
Kai protein oscillator as cyanobacterial circadian clock

Takao Kondo
Graduate School of Science, Nagoya University and CREST-JST, Nagoya , Japan

Abstract:
We reconstituted the self-sustainable circadian oscillation of phosphorylation state of the cyanobacterial clock protein KaiC by incubating it with KaiA, KaiB, and ATP. This in vitrooscillation persisted robustly and the period was compensated against temperature changes. Period lengths observed in vivo in various kaiC mutants were consistent with those measured using in vitro mixtures containing the respective mutant KaiC proteins. These results indicates that the oscillation of KaiC phosphorylation is the primary pacemaker of the cyanobacterial circadian clock.
We then found that the interactions between KaiA or KaiB with KaiC and mutual regulations of two neighboring phosphorylations of KaiC facilitated the phosphorylation cycle. Moreover, we showed that KaiC possesses extremely weak but temperature-compensated ATPase activity (15 ATPs per day) and that activities of wild-type KaiC and five period-mutant proteins are directly proportional to their in vivo circadian frequencies, indicating that the ATPase activity defines the circadian period. Based on these observations, we propose the KaiC ATPase activity as the most fundamental reaction underlying circadian periodicity of cyanobacteria.
Moreover, KaiC also has novel mechanisms for synchronization. Firstly, the robustness of the KaiC phosphorylation rhythm arises from the rapid synchronization of the phosphorylation state of KaiC proteins. This function would be crucial for the KaiC cycle to sustain its roubustness in the cell where de nove KaiC was added in the intracellular KaiC pool. Secondly, we recently found that the KaiC phosphorylation cycle can be entrained by high/low temperature cycle. Supprisingly, the pattern of entrainment was almost identical to parametric entrainment found in various eukaryotes. Thus, the Kai protein clock is inheritantly designed as the master pacemaker of cyanobacterial circadian clock.

References:
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(3) Kondo T , Mori T, Lebedeva NV, Aoki S, Ishiura M, Golden SS. (1997) Circadian rhythms in rapidly dividing cyanobacteria. Science 275: 224-227

(4) Ouyang, Y, Andersson, CA, Kondo T , Golden SS, Johnson CH. (1998) Resonating circadian clocks enhance fitness in cyanobacteria. Proc. Natl. Acad. Sci. 95: 8660-8664

(5) Ishiura M, Kutsuna S, Aoki S, Iwasaki H, Andersson, CA, Tanabe A, Golden SS, Johnson CH, Golden SS Kondo T (1998) Expression of a gene cluster kaiABC as a circadian feedback process in cyanobacteria. Science 281: 1519-1523

(6) Iwasaki H, Williams SB, Kitayama Y, Ishiura M, Golden SS, Kondo T (2000) A KaiC-interacting sensory histidine kinase, SasA, necessary to sustain robust circadian oscillation in cyanobacteria. Cell 101: 223-233

(7) Nakahira Y, Katayama M, Miyashita H, Kutsuna S, Iwasaki H, Oyama T, Kondo T (2004) Global gene repression by KaiC as a master process of prokaryotic circadian system. Proc. Natl. Acad. Sci. 101:881-5.

(8) Tomita, J, Nakajima M, Kondo T , Iwasaki H (2005) No transcription-translation feedback in circadian rhythm of KaiC phosphorylation. Science 307: 251-254

(9) Nakajima M, Imai K, Ito H, Nishiwaki T, Murayama Y, Iwasaki H, Oyama T, Kondo T . (2005) Reconstitution of Circadian Oscillation of Cyanobacterial KaiC Phosphorylation in vitro. Science 308, 414-5

(10) Nishiwaki,T, Satomi Y, Kitayama Y, Terauchi K, Kiyohara R, Takao Toshifumi, Kondo T ( 2007 ) A sequential program of dual phosphorylation of KaiC as a basis for circadian rhythm in cyanobacteria. EMBO J (2007) 26, 4029-4037

(11) Terauchi K, Kitayama Y, Nishiwaki T, Miwa K, Murayama Y, Oyama T, Kondo T. (2007) The ATPase activity of KaiC determines the basic timing for circadian clock of cyanobacteria. Proc. Natl Acad. Sci. USA. 104, 16377-16381

(12) Ito H, Kageyama H, Mutsuda M, Nakajima M, Oyama T, Kondo T(2007) Origin of the resilience of the cyanobacterial circadian clock, Nature Struct Mol Biol 14, 1084-1088

(13) Kondo T (2008) A cyanobacterial circadian clock based on the Kai oscillator In Clocks and Rhythms Edited By Stillman B and , Stewart D,  Cold Spring Harbor Laboratory press

(14) Kitayama Y, Nishiwaki T, Terauchi K, Kondo T. (2008) Dual KaiC-based oscillations constitute the circadian system of cyanobacteria, Genes & Development. 22, 1513-1521

(15) Yoshida T, Murayama Y, Ito H, Kageyama H, Kondo T (2009) Non-parametric entrainment of the in vitro circadian phosphorylation rhythm of cyanobacterial KaiC by temperature cycle PNAS106 , 1648-1653

シアノバクテリアの論文を示した。広範な生物時計の総説は 13 の単行本が最も充実している