Fig. 1.

Two feedback loops that define the circadian rhythm in Danaus plexippus. Adapted from S Zhan et al. [5]. In the first feedback loop (green proteins), the CLK:CYC dimer promotes the transcription of Per, Tim and Cry2. PER, TIM and CRY2 proteins enter the nucleus where a PER:CRY2 dimer inhibits the binding of the CLK:CYC dimer to E-Boxes and thus inhibits the expression of genes with E-Box promoters. In the second, modulatory feedback loop (yellow proteins), the CLK:CYC dimer promotes the transcription of Vri and /or Pdp1. VRI and PDP1 proteins enter the nucleus, where PDP1 promotes Clk transcription while VRI inhibits Clk transcription