%0 Journal Article %A Clerico, Eugenia M. %A Cassone, Vincent M. %A Golden, Susan S. %T Stability and lability of circadian period of gene expression in the cyanobacterium Synechococcus elongatus %D 2009 %J Microbiology, %V 155 %N 2 %P 635-641 %@ 1465-2080 %R https://doi.org/10.1099/mic.0.022343-0 %K CT, circadian time %K LL, constant light %K WT, wild-type %I Microbiology Society, %X 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. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.022343-0