Elevated ATPase Activity of KaiC Constitutes a Circadian Checkpoint of Cell Division in Synechococcus elongatus

Abstract

A circadian clock coordinates physiology and behavior in diverse groups of living organisms. Another major cyclic cellular event, the cell cycle, is regulated by the circadian clock in the few cases where linkage of these cycles has been studied. In the cyanobacterium Synechococcus elongatus, the circadian clock gates cell division by an unknown mechanism. Using timelapse microscopy, we confirm the gating of cell division in the wild-type and demonstrate the regulation of cytokinesis by key clock components. Specifically, a state of the oscillator protein KaiC that is associated with elevated ATPase activity closes the gate by acting through a known clock output pathway to inhibit FtsZ ring formation at the division site. An activity that stimulates KaiC phosphorylation independently of the KaiA protein was also uncovered. We propose a model that separates the functions of KaiC ATPase and phosphorylation in cell division gating and other circadian behaviors.