Figure 1.

Global circadian regulation of transcriptional activities in cyanobacteria. Representations of rhythmic waveforms from a promoter trap experiment (Liu et al., 1995) and the effect of KaiC overexpression on promoter activities (Nakahira et al., 2004) are shown in (A) and (B). Promoter activity was measured as luminescence from a bacterial luciferase (luxAB) reporter. (A) “Clock-dominated” genes. Waveforms representing both class 1 and class 2 promoter activities are shown. Promoters of clock-dominated genes display a high peak-to-trough amplitude with a relatively low basal level of activity. Overexpression of KaiC (lower panel, ± KaiC Ox) causes the high-amplitude waveform of these promoters to be abolished, and only low basal activity is observed (dashed line). (B) “Clock-modulated” genes. Promoters of clock-modulated genes display waveforms of luxAB expression with a low peak-to-trough amplitude but with a relatively high basal activity. Overexpression of KaiC abolishes the rhythmic expression, but a relatively high, nonrhythmic basal promoter activity remains (dashed line).