Abstract
Cyanobacterium Synechococcus elongatus PCC. 7942 is a simplest organism known to show circadian rhythm. Circadian clock of cyanobacterium can be reconstituted in vitro; robust circadian rhythm in KaiC phosphorylation is generated by mixing KaiA, KaiB, and KaiC. Phosphorylation state of KaiC is regulated by its autophosphorylation and autodephosphorylation activities. KaiC exists as a hexamer in the presence of ATP. ATP molecules bind at the interfaces of between subunits and phosphorylate S431 and T432 in the neighboring subunits. KaiC has two P-loops, which is conserved in catalytic sites of ATPases and protein kinases, however, KaiC shares no homology with protein phosphatases.
Autodephosphorylation of KaiC has not fully been studied so far. In order to examine whether KaiC dephosphorylates itself by simlar mechanism to known protein phosphatases, we phosphorylated KaiC in the presence of radioactive ATP and chased the dephosphorylation process. Based on the results, we will discuss the autodephosphorylation mechanism of KaiC.
