Abstract
Cyanobacteria are photosynthetic prokaryotes with a circadian system. In cyanobacteria, kaiA, kaiB and kaiC are known as the central genes of circadian clock genes. KaiC has an autokinase and an autophosphatase activity. KaiA and KaiB enhance KaiC autophosphorylation and autodephosphorylation, respectively. These regulatory systems form a KaiC phosphorylation cycle with a ~24-h period. The circadian changes in molecular states are converted to the transcriptional regulation in the cell. The transcriptional activities of kaiB,kaiC are under the feedback regulation of KaiC and they show a circadian rhythm. These results have been obtained from researches using a freshwater cyanobacterium, Synechococcus elongatus PCC 7942.
It was reported that a group of marine cyanobacteria, Prochlorococcus species lack kaiA in their genomes, and their circadian rhythms disappear in constant conditions. In order to verify the function of their kaiB and kaiC in diurnal system, we have tried to analyze their physiological roles in a heterologous circadian systems by introducing various constructs of Prochlorococcus kaiB and kaiC into Synechococcus cells.
