A unified mode of epigenetic gene silencing: RNA meets polycomb group proteins.

Recently, an essential role for RNA in the epigenetic silencing of genes packaged within heterochromatin in animals has been recognized. The RNA appears to be involved in targeting chromatin remodeling activity to a specific locus and in later maintaining the repressed state of the gene. Epigenetic silencing of Hox cluster genes by the Polycomb group proteins also involves the formation of a stably inherited repressive chromatin structure. Recent studies of the C. elegans PcG gene sop-2 reveled an evolutionarily conserved property of PcG proteins in the binding of RNA, suggesting an important role for RNA in PcG-mediated Hox gene repression.