The locations of chromatin loops in Drosophila were determined by Hi-C (chemical 
cross-linking, restriction digestion, ligation, and high-throughput DNA 
sequencing). Whereas most loop boundaries or "anchors" are associated with CTCF 
protein in mammals, loop anchors in Drosophila were found most often in 
association with the polycomb group (PcG) protein Polycomb (Pc), a subunit of 
polycomb repressive complex 1 (PRC1). Loops were frequently located within 
domains of PcG-repressed chromatin. Promoters located at PRC1 loop anchors 
regulate some of the most important developmental genes and are less likely to 
be expressed than those not at PRC1 loop anchors. Although DNA looping has most 
commonly been associated with enhancer-promoter communication, our results 
indicate that loops are also associated with gene repression.