Abstract
Cyanobacteria are the simplest organisms known to exhibit circadian rhythms. Three clock proteins, KaiA, KaiB, and KaiC, have been identified as essential components of the circadian oscillation, and Kai-based chemical oscillation is thought to be the basic circadian pacemaker in Synechococcus elongatus PCC 7942. Transcription and translation of kaiBC in cyanobacterial cells were quantitatively studied to elucidate how these processes were coupled to the chemical oscillator using a strain in which endogenous kaiBC was inactivated and these genes were exogenously expressed under control of the E.coli trc promoter. After addition or removal of IPTG, temporal profiles of kaiBC mRNA accumulation, KaiC protein accumulation and phosphorylation, and luxAB mRNA accumulation driven from the kaiBC promoter were quantitatively examined. Kinetic responses demonstrate the basic properties of cyanobacterial regulation of clock gene expression and indicate that both accumulation and phosphorylation of KaiC regulate kaiBC promoter activity in different fashions.
