Figure 3

Rhythms continue in the presence of transcription inhibitors. (A) A combination of actinomycin D and cordycepin reduces RNA synthesis rates to around 5% (mean ± SD, n = 4) of the values of vehicle treated cultures. Cultures survive three to five days at these concentrations of inhibitors. (B) There is no change in the timing of the bioluminescence rhythm in constant dark. Horizontal bars indicate the light regime, with drugs added to the cultures at the indicated times (red arrows). Each data point is the average of three samples. (C) There is no change in the timing of the pH rhythm used to monitor CO₂ fixation. A representative example of three different experiments is shown for each treatment. The amplitude of the rhythm is severely diminished by the third day of treatment with inhibitors. SD, standard deviation.