title: Phase-dependent generation and transmission of time information by the KaiABC circadian clock oscillator through SasA-KaiC interaction in cyanobacteria.
abstract: 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.
authors.affiliation: Center for Gene Research, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi 464-8602, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Valencia S
authors.forename: Kyouhei
authors.initials: K
authors.lastname: Bitou
authors.forename: Kentaro
authors.initials: K
authors.lastname: Ishii
authors.forename: Reiko
authors.initials: R
authors.lastname: Murakami
authors.forename: Megumi
authors.initials: M
authors.lastname: Morishita
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Onai
authors.forename: Yukio
authors.initials: Y
authors.lastname: Furukawa
authors.forename: Katsumi
authors.initials: K
authors.lastname: Imada
authors.forename: Keiichi
authors.initials: K
authors.lastname: Namba
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ishiura
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D020134:Catalytic Domain; D057906:Circadian Clocks / Q000502:physiology*; D056925:Circadian Rhythm Signaling Peptides and Proteins / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114270:KaiB protein, cyanobacteria; C114271:KaiC protein, cyanobacteria