The itty-bitty time machine genetics of the cyanobacterial circadian clock.

The cyanobacterium Synechococcus elongatus PCC 7942 has been used as the prokaryotic model system for the study of circadian rhythms for the past two decades. Its genetic malleability has been instrumental in the discovery of key input, oscillator, and output components and has also provided monumental insights into the mechanism by which proteins function to maintain and dictate 24-h time. In addition, basic research into the prokaryotic system has led to interesting advances in eukaryotic circadian mechanisms.

A novel allele of kaiA shortens the circadian period and strengthens interaction of oscillator components in the cyanobacterium Synechococcus elongatus PCC 7942.

The basic circadian oscillator of the unicellular fresh water cyanobacterium Synechococcus elongatus PCC 7942, the model organism for cyanobacterial circadian clocks, consists of only three protein components: KaiA, KaiB, and KaiC. These proteins, all of which are homomultimers, periodically interact to form large protein complexes with stoichiometries that depend on the phosphorylation state of KaiC. KaiA stimulates KaiC autophosphorylation through direct physical interactions.

Proteins found in a CikA interaction assay link the circadian clock, metabolism, and cell division in Synechococcus elongatus.

Diverse organisms time their cellular activities to occur at distinct phases of Earth's solar day, not through the direct regulation of these processes by light and darkness but rather through the use of an internal biological (circadian) clock that is synchronized with the external cycle. Input pathways serve as mechanisms to transduce external cues to a circadian oscillator to maintain synchrony between this internal oscillation and the environment. The circadian input pathway in the cyanobacterium Synechococcus elongatus PCC 7942 requires the kinase CikA.

Viral photosynthetic reaction center genes and transcripts in the marine environment.

Cyanobacteria of the genera Synechococcus and Prochlorococcus are important contributors to photosynthetic productivity in the open ocean. The discovery of genes (psbA, psbD) that encode key photosystem II proteins (D1, D2) in the genomes of phages that infect these cyanobacteria suggests new paradigms for the regulation, function and evolution of photosynthesis in the vast pelagic ecosystem. Reports on the prevalence and expression of phage photosynthesis genes, and evolutionary data showing a potential recombination of phage and host genes, suggest a model in which phage photosynthesis genes help support photosynthetic activity in their hosts during the infection process.

Winding up the cyanobacterial circadian clock.

The endogenous circadian clock of the cyanobacterium Synechococcus elongatus controls many cellular processes and confers an adaptive advantage on this organism in a competitive environment. To be advantageous, this internal biological oscillator must be reset daily to remain in synchrony with its environment and to transduce temporal information to control behaviors at appropriate times of day. Recent studies have discovered new components of these input and output pathways of the clock that help to 'wind up' our understanding of the clock system as a whole.

Detection of rhythmic bioluminescence from luciferase reporters in cyanobacteria.

The unicellular cyanobacterium Synechococcus elongatus PCC 7942 is the model organism for studying prokaryotic circadian rhythms. Although S. elongatus does not display an easily measurable overt circadian behavior, its gene expression is under circadian control; hence, a "behavior" is created by linking a cyanobacterial promoter to either the bacterial luxAB or firefly luc luciferase genes to create reporter fusions whose activity can be easily monitored by bioluminescence.