Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 104, Issue 47, Pages 18819-18824Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0706069104
Keywords
DNA topology; gene expression; supercoiling; biological clock
Categories
Funding
- NIGMS NIH HHS [R01 GM067152, R37 GM067152] Funding Source: Medline
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The cyanobacterium Synechococcus elongatus expresses robust circadian (daily) rhythms under the control of the KaiABC-based core clockwork. Unlike eukaryotic circadian systems characterized thus far, the cyanobacterial clockwork modulates gene expression patterns globally and specific clock gene promoters are not necessary in mediating the circadian feedback loop. The oscilloid model postulates that global rhythms of transcription are based on rhythmic changes in the status of the cyanobacterial chromosome that are ultimately controlled by the KaiABC oscillator. By using a nonessential, cryptic plasmid (pANS) as a reporter of the superhelical state of DNA in cyanobacteria, we show that the supercoiling status of this plasmid changes in a circadian manner in vivo. The rhythm of topological change in the plasmid is conditional; this change is rhythmic in constant light and in light/dark cycles, but not in constant darkness. In further support of the oscilloid model, cyanobacterial promoters that are removed from their native chromosomal locations and placed on a plasmid preserve their circadian expression patterns.
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