Regulation of Polycomb group genes Psc and Su(z)2 in Drosophila melanogaster

► Four PcG binding sites were tested for autonomous PRE activity. ► Two have classical PRE activity. ► One has an unusual downregulating activity and inverse dependence on PC. ► Deletion of one binding site causes a weak derepression. ► A presumptive insulator prevents silencing of flanking genes.