Bacterial circadian programs.
Twenty years ago, it was widely believed that prokaryotes were too "simple" to have evolved circadian programs. Since that time, however, the cyanobacterial circadian system has progressed from a curiosity to a major model system for analyzing clock phenomena. In addition to globally regulating gene expression, cyanobacteria are one of the only systems in which the adaptive fitness of a circadian system has been rigorously evaluated. Moreover, cyanobacteria are the only clock system in which all essential proteins of the core oscillator have been crystallized and structurally determined, namely, the KaiA, KaiB, and KaiC proteins. A biochemical oscillator can be reconstituted in vitro with these three purified Kai proteins and displays the key properties of temperature-compensated rhythmicity. This result spectacularly demonstrates that a strictly posttranslational clock is sufficient to elaborate circadian phenomena and that a transcription-translation feedback loop is not obligatory. The conjunction of structural information on essential clock proteins with a defined system that reconstitutes circadian oscillations in vitro leads to a turning point whereby biophysical and biochemical approaches bring analyses of circadian clock-work to an unprecedented level of molecular detail.
Johnson
C H
CH
Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235, USA.
D000222:Adaptation, Physiological; D001419:Bacteria / Q000166:cytology / Q000235:genetics*; D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D002455:Cell Division / Q000235:genetics / Q000502:physiology; D002940:Circadian Rhythm / Q000235:genetics* / Q000502:physiology*; D056925:Circadian Rhythm Signaling Peptides and Proteins; D000458:Cyanobacteria / Q000235:genetics / Q000502:physiology; D025461:Feedback, Physiological; D015870:Gene Expression; D005798:Genes, Bacterial; D008954:Models, Biological; D008958:Models, Molecular; D005810:Multigene Family
D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114269:KaiA protein, cyanobacteria; C114270:KaiB protein, cyanobacteria; C114271:KaiC protein, cyanobacteria