This Article Full Text Full Text (PDF) Supplemental material Other Versions of this Article: JB.01693-07v1 190/5/1691    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Murayama, Y. Articles by Kondo, T. Search for Related Content PubMed PubMed Citation Articles by Murayama, Y. Articles by Kondo, T.

 Previous Article  |  Next Article 

Journal of Bacteriology, March 2008, p. 1691-1698, Vol. 190, No. 5
0021-9193/08/$08.00+0     doi:10.1128/JB.01693-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Regulation of Circadian Clock Gene Expression by Phosphorylation States of KaiC in Cyanobacteria ^,

Division of Biological Science, Graduate School of Science, Nagoya University and SORST/CREST, Japan Science and Technology Agency, Furo-cho 1, Chikusa-ku, Nagoya 464-8602, Japan

Received 21 October 2007/ Accepted 17 December 2007

Three clock proteins—KaiA, KaiB, and KaiC—have been identified as essential components of the circadian oscillator in cyanobacteria, and Kai-based chemical oscillation is thought to be the basic circadian timing mechanism in Synechococcus elongatus PCC 7942. Transcription and translation of kaiBC in cyanobacterial cells was quantitatively studied to elucidate how these processes are coupled to the chemical oscillator using a strain in which circadian oscillation is under the control of IPTG (isopropyl-β-D-thiogalactopyranoside). The kinetics of repression of kaiBC promoter triggered by IPTG allowed estimation of transient response at 10 h. This response time is suitable for cyanobacterial transcription and/or translation to match with the Kai-based oscillator. Interestingly, kaiBC promoter activity and KaiC phosphorylation showed robust circadian rhythms, whereas trc promoter-driven kaiBC mRNA levels and KaiC accumulation were almost arrhythmic. These results indicate that cyanobacterial circadian rhythms can be generated even if kaiBC expression is constitutive. Moreover, there was a positive correlation between activation of the kaiBC promoter and an increase in the KaiC phosphorylation ratio in three rhythmic conditions. Based on these observations, it is likely that the KaiC phosphorylation ratio is the main factor in the activation of kaiBC promoter. Finally, we quantitatively compared the threshold level of phosphorylated KaiC for the repression or derepression of kaiBC promoter and found that this parameter is an important factor in repressing the kaiBC promoter.

Published ahead of print on 28 December 2007.

Supplemental material for this article may be found at http://jb.asm.org/.