Investigation for the Role of KaiC Phosphorylation in Circadian Clock System of Synechococcus elongatus PCC7942

Abstract

In the cyanobacterium Synechococcus elongatus PCC 7942, kaiA, kaiB and kaiC have been found to be essential for the circadian rhythm generation. KaiC is proposed as a negative regulator of autoregulatory circadian kaiBC expression, a presumable key process to generate circadian oscillations. KaiC undergoes circadian Ser/Thr-phosphorylation in vivo and has an autokinase/autophosphatase activity in vitro. The magnitude of KaiC phosphorylation is enhanced and negated by KaiA and KaiB, respectively, both in vitro and in vivo. However, functions of KaiC phosphorylation in the circadian rhythm generation still remain unknown. We obtained two kaiC mutant strains in which the phosphorylation level of KaiC was reduced. These mutations abolished the circadian kaiBC expression rhythm. We are also trying to identify phosphorylation sites of KaiC. Based on these results, possible roles of KaiC phosphorylation in the