Insulators; not Polycomb Response Elements; are required for long-range interactions between Polycomb targets in Drosophila

Hua-Bing Li; Martin Müller; Ilham Anne Bahechar; Olga Kyrchanova ; Katsuhito Ohno; Pavel Georgiev and Vincenzo Pirrotta Rutgers University Molecular and Cellular Biology 31 (4) (2010)