Expression of a Gene Cluster kaiABC as a Circadian Feedback Process in Cyanobacteria

• DOI: 10.1126/science.281.5382.1519
• Publication Date: 2002-07-27T09:35:26Z
• Authors: Masahiro Ishiura; Shinsuke Kutsuna; Setsuyuki Aoki; Hideo Iwasaki; Carol R. Andersson; Akio Tanabe; Susan S. Golden; Carl H. Johnson; Takao Kondo
• Keywords: 0301 basic medicine; Luminescence; Transcription, Genetic; Circadian Rhythm Signaling Peptides and Proteins; Recombinant Fusion Proteins; Molecular Sequence Data; Gene Expression Regulation, Bacterial; Cyanobacteria; Models, Biological; Circadian Rhythm; Feedback; 03 medical and health sciences; Bacterial Proteins; Biological Clocks; Genes, Bacterial; Genes, Reporter; Multigene Family; Mutation; Amino Acid Sequence; Cloning, Molecular; Promoter Regions, Genetic

Cyanobacteria are the simplest organisms known to have a circadian clock. A circadian clock gene cluster kaiABC was cloned from the cyanobacterium Synechococcus. Nineteen clock mutations were mapped to the three kai genes. Promoter activities upstream of the kaiA and kaiB genes showed circadian rhythms of expression, and both kaiA and kaiBC messenger RNAs displayed circadian cycling. Inactivation of any single kai gene abolished these rhythms and reduced kaiBC -promoter activity. Continuous kaiC overexpression repressed the kaiBC promoter, whereas kaiA overexpression enhanced it. Temporal kaiC overexpression reset the phase of the rhythms. Thus, a negative feedback control of kaiC expression by KaiC generates a circadian oscillation in cyanobacteria, and KaiA sustains the oscillation by enhancing kaiC expression.