Molecular Mechanisms of Polycomb Silencing
Yuri B. Schwartz and Vincenzo Pirrotta
from: Epigenetics (Edited by: Jörg Tost). Caister Academic Press, U.K. (2008)
Polycomb and Trithorax group proteins have long been known as important epigenetic regulators of homeotic genes. Recent advances in genome-wide mapping techniques have uncovered their broad role in cell differentiation, which is exerted through the direct control of hundreds of transcription factors as well as important signaling proteins and morphogens. Polycomb silencing, originally believed to result from stable packaging of chromatin is now viewed as dynamic process intimately dependent on histone modifications and balanced by antagonistic action of Trithorax proteins. Recruitment of Polycomb proteins (PcG) to chromatin is mediated by Polycomb Response Elements (PREs), DNA sequence elements found in the vicinity of PcG target genes. These elements are thought to contain a collection of binding sites for sequence-specific DNA binding proteins that assemble PcG complexes. PREs serve as binding hubs where Polycomb proteins remain localized but loop over to interact with the promoters and other parts of target genes read more ...