Figure 6.

Schematic model for the action of dual elements. (A) PREs can silence gene expression by acting at a distance within a three-dimensional topology that silences promoter activity (top panel) or directly at the promoter (middle panel) to silence transcription. (Bottom panel) Our data suggest a third mode, where PcG acts locally to silence a PRE/enhancer dual-element activity, leaving the promoter still available for activation by another enhancer (see also Fig. 1F). (B) A dual element can act as a PRE (top panel) in one cell context through the recruitment of the PcG system (purple ellipsoid) to silence gene expression, while, in another context, the same element can act as an enhancer (bottom panel) through the recruitment of tissue-specific TFs (green spheres) to initiate spatio–temporal gene expression.