title: Origin and evolution of circadian clock genes in prokaryotes.
abstract: Regulation of physiological functions with approximate daily periodicity, or circadian rhythms, is a characteristic feature of eukaryotes. Until recently, cyanobacteria were the only prokaryotes reported to possess circadian rhythmicity. It is controlled by a cluster of three genes: kaiA, kaiB, and kaiC. Using sequence data of approximately 70 complete prokaryotic genomes from the various public depositories, we show here that the kai genes and their homologs have quite a different evolutionary history and occur in Archaea and Proteobacteria as well. Among the three genes, kaiC is evolutionarily the oldest, and kaiA is the youngest and likely evolved only in cyanobacteria. Our data suggest that the prokaryotic circadian pacemakers have evolved in parallel with the geological history of the earth, and that natural selection, multiple lateral transfers, and gene duplications and losses have been the major factors shaping their evolution.
authors.affiliation: Institute of Evolution, University of Haifa, Mount Carmel, Haifa 31905, Israel.
authors.forename: Volodymyr
authors.initials: V
authors.lastname: Dvornyk
authors.forename: Oxana
authors.initials: O
authors.lastname: Vinogradova
authors.forename: Eviatar
authors.initials: E
authors.lastname: Nevo
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D001683:Biological Clocks / Q000235:genetics / Q000502:physiology; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology; D056925:Circadian Rhythm Signaling Peptides and Proteins; D000458:Cyanobacteria / Q000235:genetics / Q000502:physiology*; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D010802:Phylogeny; D011110:Polymorphism, Genetic; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114269:KaiA protein, cyanobacteria; C114270:KaiB protein, cyanobacteria; C114271:KaiC protein, cyanobacteria