CikA, a Bacteriophytochrome That Resets the Cyanobacterial Circadian Clock

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Science  04 Aug 2000:
Vol. 289, Issue 5480, pp. 765-768
DOI: 10.1126/science.289.5480.765

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The circadian oscillator of the cyanobacterium Synechococcus elongatus, like those in eukaryotes, is entrained by environmental cues. Inactivation of the gene cikA (circadian input kinase) shortens the circadian period of gene expression rhythms inS. elongatus by approximately 2 hours, changes the phasing of a subset of rhythms, and nearly abolishes resetting of phase by a pulse of darkness. The CikA protein sequence reveals that it is a divergent bacteriophytochrome with characteristic histidine protein kinase motifs and a cryptic response regulator motif. CikA is likely a key component of a pathway that provides environmental input to the circadian oscillator in S. elongatus.

  • * Present address: Botanisches Institut, University of Cologne, Gyrhofstrasse 15, 50931 Cologne, Germany.

  • To whom correspondence should be addressed. E-mail: sgolden{at}

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