Editors' ChoiceCircadian Cycle

Clock Components

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Science's STKE  08 Aug 2000:
Vol. 2000, Issue 44, pp. tw3
DOI: 10.1126/stke.2000.44.tw3

The core components of the molecular clocks that underlie circadian rhythms in animals, fungi, and bacteria appear to be in hand, but for plants and cyanobacteria, key elements are still being elucidated, including components that respond to changes in day length. Schmitz et al. identified a bacteriophytochrome in the cyanobacterium Synechoccus elongatus that helps the clock respond to environmental clues. The CikA (for circadian input kinase) gene appears to be critical for resetting the phase of the clock after a period of darkness. Working with rhythm mutants in the plant Arabidopsis, Strayer et al. have now cloned the gene TOC1, which regulates the period of the circadian cycle in the absence of input from light. Because this gene is itself regulated by a feedback loop subject to circadian influences, it helps the plant respond to changes in day length. The predicted TOC1 protein has some intriguing features, including similarity to transcription factors and two-component signal transduction systems.

Schmitz, O., Katayama, M., Williams, S.B., Kondo, T., and Golden, S.S. (2000) CikA, a bacteriophytochrome that resets the cyanobacterial circadian clock. Science 289: 765-768. [Abstract] [Full Text]

Strayer, C., Oyama, T., Schultz, T.F., Raman, R., Somer, D.E., Más, P., Panda, S., Kreps, J.A., and Kay, S.A. (2000) Cloning of the Arabidopsis clock gene TOC1, an autoregulatory response regulator homolog. Science 289: 768-771. [Abstract] [Full Text]

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