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Stability and lability of circadian period of gene expression in the cyanobacterium Synechococcus elongatus

Eugenia M. Clerico

Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX 77843-3258, USA

Correspondence
Susan S. Golden
sgolden{at}tamu.edu

Molecular aspects of the circadian clock in the cyanobacterium Synechococcus elongatus have been described in great detail. Three-dimensional structures have been determined for the three proteins, KaiA, KaiB and KaiC, that constitute a central oscillator of the clock. Moreover, a temperature-compensated circadian rhythm of KaiC phosphorylation can be reconstituted in vitro with the addition of KaiA, KaiB and ATP. These data suggest a relatively simple circadian system in which a single oscillator provides temporal information for all downstream processes. However, in vivo the situation is more complex, and additional components contribute to the maintenance of a normal period, the resetting of relative phases of circadian oscillations, and the control of rhythms of gene expression. We show here that two well-studied promoters in the S. elongatus genome report different circadian periods of expression under a given set of conditions in wild-type as well as mutant genetic backgrounds. Moreover, the period differs between these promoters with respect to modulation by light intensity, growth phase, and the presence or absence of a promoter-recognition subunit of RNA polymerase. These data contrast sharply with the current clock model in which a single Kai-based oscillator governs circadian period. Overall, these findings suggest that complex interactions among the circadian oscillator, perhaps other oscillators, and other cellular machinery result in a clock that is plastic and sensitive to the environment and to the physiological state of the cell.

Present address: Department of Biochemistry and Molecular Biology, University of Massachusetts, Lederle Research Graduate Tower, 710 North Pleasant St, Amherst, MA 01003, USA.

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				Y. Chen, Y.-I. Kim, S. R. Mackey, C. K. Holtman, A. LiWang, and S. S. Golden A Novel Allele of kaiA Shortens the Circadian Period and Strengthens Interaction of Oscillator Components in the Cyanobacterium Synechococcus elongatus PCC 7942 J. Bacteriol., July 1, 2009; 191(13): 4392 - 4400. [Abstract] [Full Text] [PDF]