title: Diversity of KaiC-based timing systems in marine Cyanobacteria.
abstract: The coordination of biological activities into daily cycles provides an important advantage for the fitness of diverse organisms. Most eukaryotes possess an internal clock ticking with a periodicity of about one day to anticipate sunrise and sunset. The 24-hour period of the free-running rhythm is highly robust against many changes in the natural environment. Among prokaryotes, only Cyanobacteria are known to harbor such a circadian clock. Its core oscillator consists of just three proteins, KaiA, KaiB, and KaiC that produce 24-hour oscillations of KaiC phosphorylation, even in vitro. This unique three-protein oscillator is well documented for the freshwater cyanobacterium Synechococcus elongatus PCC 7942. Several physiological studies demonstrate a circadian clock also for other Cyanobacteria including marine species. Genes for the core clock components are present in nearly all marine cyanobacterial species, though there are large differences in the specific composition of these genes. In the first section of this review we summarize data on the model circadian clock from S. elongatus PCC 7942 and compare it to the reduced clock system of the marine cyanobacterium Prochlorococcus marinus MED4. In the second part we discuss the diversity of timing mechanisms in other marine Cyanobacteria with regard to the presence or absence of different components of the clock.
authors.affiliation: Institute for Theoretical Biology, Charité - Universitätsmedizin, Invalidenstraße 43, D-10115 Berlin, Germany; Institute for Synthetic Microbiology, Heinrich Heine University Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany. Electronic address: ilka.axmann@hhu.de.
authors.forename: Ilka M
authors.initials: IM
authors.lastname: Axmann
authors.affiliation: Institute for Theoretical Biology, Charité - Universitätsmedizin, Invalidenstraße 43, D-10115 Berlin, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Hertel
authors.affiliation: Institute for Theoretical Biology, Charité - Universitätsmedizin, Invalidenstraße 43, D-10115 Berlin, Germany.
authors.forename: Anika
authors.initials: A
authors.lastname: Wiegard
authors.affiliation: Institute for Microbiology and Molecular Biology, Justus Liebig University Gießen, Heinrich-Buff-Ring 26, D-35392 Gießen, Germany.
authors.forename: Anja K
authors.initials: AK
authors.lastname: Dörrich
authors.affiliation: Institute of Biology, University of Freiburg, Schänzlestraße 1, D-79104 Freiburg, Germany.
authors.forename: Annegret
authors.initials: A
authors.lastname: Wilde
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D057906:Circadian Clocks / Q000235:genetics* / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D056925:Circadian Rhythm Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000502:physiology*; D014644:Genetic Variation; D008969:Molecular Sequence Data; D010766:Phosphorylation; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114271:KaiC protein, cyanobacteria
keywords: Circadian clock; Diversity; KaiC; Marine Cyanobacteria