Masahiro Ishiura,
*
Shinsuke Kutsuna,
Setsuyuki Aoki,
Hideo Iwasaki,
Carol R. Andersson,
Akio Tanabe,
Susan S. Golden,
Carl H. Johnson,
Takao Kondo
*
Cyanobacteria are the simplest organisms known to have a circadian
clock. A circadian clock gene cluster kaiABC was cloned from
the cyanobacterium Synechococcus. Nineteen clock mutations were mapped to the three kai genes. Promoter activities
upstream of the kaiA and kaiB genes showed
circadian rhythms of expression, and both kaiA and
kaiBC messenger RNAs displayed circadian cycling. Inactivation of any single kai gene abolished these rhythms
and reduced kaiBC-promoter activity. Continuous
kaiC overexpression repressed the kaiBC
promoter, whereas kaiA overexpression enhanced it. Temporal
kaiC overexpression reset the phase of the rhythms. Thus, a
negative feedback control of kaiC expression by KaiC
generates a circadian oscillation in cyanobacteria, and KaiA sustains
the oscillation by enhancing kaiC expression.
M. Ishiura, S. Kutsuna, S. Aoki, H. Iwasaki, A. Tanabe, T. Kondo,
Division of Biological Science, Graduate School of Science, Nagoya
University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan. C. R. Andersson and S. S. Golden, Department of Biology, Texas A&M
University, College Station, TX 77843, USA. C. H. Johnson,
Department of Biology, Vanderbilt University, Nashville, TN 37235, USA.
*
To whom correspondence should be addressed. E-mail: ishiura (or kondo)
@bio.nagoya-u.ac.jp
Present address: Division of Biological Informatics, Graduate
School of Human Informatics, Nagoya University, Chikusa-ku, Nagoya,
Aichi 464-8601, Japan.
Present address: Department of Cell Biology, Scripps Research
Institute, 10550 North Torrey Pines Road, La Jolla, CA, 92037, USA.
