Drosophila melanogaster Raw sequence reads. Drosophila melanogaster

Polycomb group response elements (PREs) in Drosophila are DNA-elements that recruit Polycomb proteins (PcG) to chromatin and regulate gene expression. PREs are easily recognizable in the Drosophila genome as strong peaks of PcG-protein binding over discrete DNA fragments; many small but statistically significant PcG peaks are also observed in the PcG domains. Surprisingly, in vivo deletion of the characterized four major PREs from the PcG regulated invected-engrailed (inv-en) gene complex did not disrupt the formation of the H3K27me3 domain and did not affect inv-en expression in embryos or larvae suggesting the presence of redundant PcG recruitment mechanism. We showed the 3D-structure of the inv-en domain was only minimally altered by the deletion of the major PREs and the domain structure involves interaction between fragments with smaller PcG peaks. A reporter construct containing a 7.5kb en fragment that contains three small peaks but no large PcG peaks forms an H3K27me3 domain and is PcG-regulated. This study establishes a model for the recruitment of PcG-complexes to Drosophila genes via interactions with multiple, minor PREs spread throughout an H3K27me3 domain.