Abstract
Circadian clock of cyanobacteria had been considerd to be composed of nagetive feedback regulation of kaiBC expression. Recently, our group reported that KaiC phosphorylation state oscillated without gene expressions, including kaiBC expression. In addition, mutants strains of Synechococcus elongatus, in which each two phsophorylation sites of KaiC was substituted for alanine, lost circadian rhythm in gene expression. These evidence indicate that phosphorylation of KaiC is more important in circadian clock of cyanobacteria than that of eukaryotic clock proteins.
We have tried to elucidate the biochemical mechanism of KaiC phosphorylation in vitro. KaiC had both autophosphorylation and autodephosphorylation activities, implying self-sustainable oscillation of KaiC phosphorylation. By the enzymatic study, it was elucidated that KaiA inhibited the dephosphorylation activity. We will report KaiC phosphorylation kinetics with more detailed biochemical analysis and the mechanism of cyanobacteria circadian clock.
