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 Ϸ70 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.

Cloning, expression, purification, crystallization and preliminary crystallographic analysis of selenomethionine-labelled KaiC-like protein PH0186 fromPyrococcus horikoshiiOT3

“…such as volcanoes, hot springs and seabeds, and the phenomenon of circadian rhythm has not yet been reported in archea. Interestingly, however, KaiC homologues have been found in some archaea such as Aeropyrum, Archaeoglobus, Halobacterium, Methanococcus, Pyrobaculum, Pyrococcus and Sulfolobus (Dvornyk et al, 2003). Most of the KaiC homologues in archea are short and single-domain.…”

“…Most of the KaiC homologues in archea are short and single-domain. The single domains usually match both domains of KaiC, but always have higher similarity to the first domain KaiCI (Dvornyk et al, 2003). The functions of these homologous genes in archea are unknown.…”

Tetrameric Architecture of the Circadian Clock Protein KaiB

“…The circadian clock gene cluster, kaiABC, was originally discovered and cloned from the cyanobacterium Synechococcus elongatus PCC7942 (6). Interestingly, kaiB and kaiC homologues of unknown function have been discovered in Archaea and Proteobacteria, but the three kai genes have very different evolutionary histories (7). In S. elongatus PCC7942, however, inactivation of any single kai gene abolishes the circadian rhythms (6).…”

Identification of human Clock gene variants by denaturing high-performance liquid chromatography

“…It is a cardinal feature of all eukaryotic, and has also been observed in some prokaryotic, organisms (Dvornyk et al 2003). The self-sustained, internal timing system is controlled endogenously but entrained by external light level.…”