Comparing two models based on the transcriptional regulation by KaiC of cyanobacteria rhythm

Circadian clocks are self-sustained biological oscillators that can be entrained by environmental cues. Cyanobacteria are the simplest organisms known to exhibit circadian rhythms, which is the fundamental process of homeostasis adapting to daily environmental changes. The cyanobacterial clock gene products, KaiA, KaiB, and KaiC interact with each other, and regulate KaiC phosphorylation and kaiBC expression in a circadian fashion. The total phosphorylation level of KaiC oscillates with a circadian period. In this paper, based on two possible transcriptional regulations, we examined numerically two models, the Transcriptional Activation Model and the Transcriptional Repression Model to generate circadian oscillation of kai genes. These two models both reproduce experimental observed sustained circadian oscillations in constant dark(DD) and constant light(LL). Comparing phase shifts between DD and LL in these two model, the Transcriptional Activation Model is consistent with the experimental observations, suggesting that the Transcriptional Activation Model may reflect the essence of the actual mechanism of kai oscillator in cyanobacteria.