title: Stability and lability of circadian period of gene expression in the cyanobacterium Synechococcus elongatus.
abstract: 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.
authors.affiliation: Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX 77843-3258, USA.
authors.forename: Eugenia M
authors.initials: EM
authors.lastname: Clerico
authors.affiliation: Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX 77843-3258, USA.
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Cassone
authors.affiliation: Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX 77843-3258, USA.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Golden
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002940:Circadian Rhythm / Q000528:radiation effects; D015964:Gene Expression Regulation, Bacterial / Q000528:radiation effects; D008027:Light; D011401:Promoter Regions, Genetic; D046940:Synechococcus / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins