The 'oscilloid' model for the circadian system of cyanobacteria. KaiA, KaiB, and KaiC are synthesized from the kaiABC cluster using two promoters: kaiAp (driving expression of KaiA) and kaiBCp (driving expression of a dicistronic mRNA encoding KaiB and KaiC). KaiA promotes the phosphorylation of KaiC and inhibits its dephosphorylation, while KaiB antagonizes the actions of KaiA. KaiC phosphorylation is coincident with the formation of a KaiC-containing complex that mediates rhythmic and global changes in the status of the chromosome. These changes in chromosomal status influence the transcriptional activity of all promoters (including kai promoters) in the chromosome so that there are global circadian changes in gene expression. Approximately 10% of promoters in the organism receive only the rhythmic input and are clock-dominated, or high-amplitude (including kaiBCp), and the remaining 90% of promoters (clock-modulated, or low-amplitude; including kaiAp) receive both rhythmic input and basal non-oscillatory input. Modified from [15,16,22].
Johnson Genome Biology 2004 5:217