How a cyanobacterium tells time.

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The cyanobacterium Synechococcus elongatus possesses a robust circadian clock mechanism.
• This clock is centered around a protein oscillator comprising KaiA, KaiB, and KaiC.
• The in vitro system can replicate the circadian rhythm of KaiC phosphorylation.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying the circadian clock in Synechococcus elongatus.
• To understand how light/dark information is relayed to the core oscillator.
• To investigate the downstream effects of the circadian clock on genomic regulation.

Main Methods:

• Characterization of KaiA, KaiB, and KaiC protein structures.
• Analysis of KaiC phosphorylation dynamics and Kai protein interactions.
• Investigation of KaiC's ATPase activity.
• Identification of input pathways involving redox-sensitive proteins and photosynthetic function.
• Study of signal transduction pathways broadcasting temporal information to the genome.

Main Results:

• The KaiA, KaiB, and KaiC protein complex recapitulates circadian rhythms of KaiC phosphorylation in vitro.
• Molecular structures of KaiA, KaiB, and KaiC are known.
• Phosphorylation steps, protein interactions, and weak ATPase activity of KaiC are characterized.
• A redox-sensitive input pathway relays light/dark signals via photosynthesis.
• Signal transduction proteins broadcast temporal information, leading to clock-regulated transcription and chromosome compaction.

Conclusions:

• The Synechococcus elongatus circadian clock is a complex system involving protein-based oscillation, light input, and genome-wide regulation.
• The core KaiA-KaiB-KaiC oscillator is sufficient to generate circadian rhythms.
• The clock influences fundamental cellular processes including gene expression and chromosome organization.