Fig 5.

Working model of KaiA protein function and its role in S. elongatus circadian timekeeping. CikA and other environmental sensors initiate signal transduction cascades that result in activation of the KaiA pseudo-receiver domain. This activation modulates the KaiA carboxyl-terminal domain's enhancement of the KaiC autophosphorylation rate. Thus, equilibria between KaiC phosphorylation states are perturbed. These states differentially control clock output, possibly through the SasA protein kinase. In this manner, a cycle of input, oscillation, and output can be established.