Regulatory relationships among TOC1 / PRR s and CCA1 / LHY. CCA1, LHY, TOC1, PRR9, PRR7, and PRR5 all are recruited to promoters and regulate transcription (yellow shading). PRR9, PRR7, and PRR5 are negative regulators (indicated in red) of CCA1 and LHY, whereas CCA1 and LHY are both negative regulators (in red) of TOC1 and positive regulators (indicated in green) of PRR7 and PRR9. PRR3 is not known to regulate transcription. Instead (blue shading), PRR3 interacts with TOC1 protein to protect it from ZTL-mediated recruitment for proteasomal degradation. Modified from .