Abstract
Cyanobacteria are photosynthetic organisms that are known to be responsible for oxygenating Earth’s early atmosphere. Having evolved to ensure optimal survival in the periodic light/dark cycle on this planet, their genetic codes are packed with various tools, including a sophisticated biological timekeeping system. Among the cyanobacteria is Synechococcus elongatus PCC 7942, the simplest clock-harboring organism with a powerful genetic tool that enabled the identification of its intricate timekeeping mechanism. The three central oscillator proteins—KaiA, KaiB, and KaiC—drive the 24 h cyclic gene expression rhythm of cyanobacteria, and the “ticking” of the oscillator can be reconstituted inside a test tube just by mixing the three recombinant proteins with ATP and Mg2+. Along with its biochemical resilience, the post-translational rhythm of the oscillation can be reset through sensing oxidized quinone, a metabolite that becomes abundant at the onset of darkness. In addition, the output components pick up the information from the central oscillator, tuning the physiological and behavioral patterns and enabling the organism to better cope with the cyclic environmental conditions. In this review, we highlight our understanding of the cyanobacterial circadian clock and discuss how it functions as a molecular chronometer that readies the host for predictable changes in its surroundings.
Highlights
The Free-Running Cyanobacterial Central OscillatorAs the Earth spins on its own axis with a 24 h periodicity as it revolves around the Sun, light and darkness take their turn, marking the start and end of a day respectively
Cyanobacteria emerged as an exception and showed a free-running oscillator component that is embedded in, yet independent from, the translation feedback loop (TTFL) known as the post-translational oscillator (PTO) [12]
Cyanobacteria rely on the circadian clock to generate a biological rhythm, staying in tune with the 24 h day/night transition in order to optimize survival and reproduction
Summary
As the Earth spins on its own axis with a 24 h periodicity as it revolves around the Sun, light and darkness take their turn, marking the start and end of a day respectively. The in vivo mutational analyses provide an initial and basic insight on It is becausevariation of this free-running the central oscillator that cyanobacteria can functional keep time, the phenotypic that resultsability from of a dysfunctional component, structural and even in a constant environment, such as constant light, which makes sure that the internal clock is analyses are needed in order to look at a more detailed picture of the biological timekeeping, unperturbed by the environment [23]. The in vivo mutational analyses provide an initial and basic insight on the phenotypic variation that results from a dysfunctional component, structural and functional analyses are needed in order to look at a more detailed picture of the biological timekeeping, phase resetting, The circadian oscillation of KaiC phosphorylation is readily detected in vitro via SDS-PAGE, wherein phosphorylated KaiC can be viewed as an upper triple band and dephosphorylated KaiC can be viewed as a lower single band on the gel [28].
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