2004 Fiscal Year Final Research Report Summary
Biochemical functions of a cyanobacterial clock protein KaiC
| Project/Area Number |
15370074
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Molecular biology
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| Research Institution | Nagoya University |
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Principal Investigator |
IWASAKI Hideo Nagoya University, Graduate School of Science, Assistant Professor, 大学院・理学研究科, 助手 (00324393)
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| Co-Investigator(Kenkyū-buntansha) |
KONDO Takao Nagoya University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (10124223)
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| Project Period (FY) |
2003 – 2004
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| Keywords | circadian / biological clock / phosphorylation / cyanobacteria / feedback / in vitro reconstitution / KaiABC / circadianal rhythm |
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| Research Abstract |
Circadian rhythms are endogenous oscillations with a period of 〜24 h and observed from bacteria to higher plants and mammals. A dogmatic model has been believed in any model organisms that circadian oscillations are driven by an autoregulatory transcription/translation feedback loops. However, we recently broke this 'Central Dogma in circadian clock research' in cyanobacteria.
Cyabacteria are the simplest organisms known to show circadian rhythms. In the cyanobacterium Synechococcus elongatus, almost all gene promoter activities show circadian rhythms. Such transcriptional rhythms require three clock genes, kaiA, kaiB are kaiC. KaiC shows circadian change in its phosphorylation state. We found in continuous dark conditions that the KaiC phosphorylation cycle sustained even after all clock gene transcripts disappeared and de novo transcription and translation were abolished in the presence of excess transcription/translation inhibitors.
KaiC has both autophosphorylation and autodephosphorylation activities that are modified by KaiA and KaiB. KaiA, KaiB and C proteins form transient complexes during a circadian cycle. Thus, we proposed that a protein dynamics among the three Kai proteins is the core of circadian timing mechanism in cyanobacteria. Indeed, we succeeded in reconstitution of circadian oscillation of KaiC phosphorylation in vitro by incubating the three Kai proteins with ATP.
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