Figure 2.—

“A schematic diagram of a cell expressing a circadian rhythm. The frq gene encodes the FRQ protein that has multiple roles, of which the best established is to regulate, probably through intermediates, the amount of frq mRNA as a part of the negative feedback loop that constitutes the circadian oscillator… . clock-controlled genes (ccgs) … CCRE, the circadian clock responsive element or “clock box” is the DNA element that mediates the action of clock-controlled transcription factors …” FRQ is now in the core loop but the loop retains notions of elements acting in sequential steps. (Figure and quotation are from Aronson et al. 1994a, p. 1582.)