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Phase‐dependent generation and transmission of time information by the KaiABC circadian clock oscillator through SasA‐KaiC interaction in cyanobacteria
Author(s) -
Valencia S. J.,
Bitou Kyouhei,
Ishii Kentaro,
Murakami Reiko,
Morishita Megumi,
Onai Kiyoshi,
Furukawa Yukio,
Imada Katsumi,
Namba Keiichi,
Ishiura Masahiro
Publication year - 2012
Publication title -
genes to cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.912
H-Index - 115
eISSN - 1365-2443
pISSN - 1356-9597
DOI - 10.1111/j.1365-2443.2012.01597.x
Subject(s) - autophosphorylation , sasa , circadian clock , biology , phosphorylation , circadian rhythm , histidine kinase , microbiology and biotechnology , biochemistry , protein kinase a , botany , gene , neuroscience , mutant
Circadian clocks allow organisms to predict environmental changes of the day/night cycle. In the cyanobacterial circadian clock machinery, the phosphorylation level and ATPase activity of the clock protein KaiC oscillate with a period of approximately 24 h. The time information is transmitted from KaiC to the histidine kinase SasA through the SasA autophosphorylation‐enhancing activity of KaiC, ultimately resulting in genome‐wide transcription cycles. Here, we showed that SasA derived from the thermophilic cyanobacterium Thermosynechococcus elongatus BP‐1 has the domain structure of an orthodox histidine kinase and that its C‐terminal domain, which contains a phosphorylation site at His160, is responsible for the autophosphorylation activity and the temperature‐ and phosphorylation state‐dependent trimerization / hexamerization activity of SasA. SasA and KaiC associate through their N‐terminal domains with an affinity that depends on their phosphorylation states. Furthermore, the SasA autophosphorylation‐enhancing activity of KaiC requires the C‐terminal ATPase catalytic site and depends on its phosphorylation state. We show that the phosphotransfer activity of SasA is essential for the generation of normal circadian gene expression in cyanobacterial cells. Numerical simulations suggest that circadian time information (free phosphorylated SasA) is released mainly by unphosphorylated KaiC during the late subjective night.