The Drosophila Polycomb protein interacts with nucleosomal core particles in vitro via its repression domain

The proteins of the Polycomb group (PcG) are required for maintaining regul ator genes, such as the homeotic selectors, stably and heritably repressed in appropriate developmental domains. It has been suggested that PcG protei ns silence genes by treating higher-order chromatin structures at their chr omosomal targets, thus preventing the interaction of components of the tran scriptional machinery with their cis-regulatory elements. An unresolved iss ue is how higher order-structures are anchored at the chromatin base, the n ucleosomal fiber. Here we show a direct biochemical interaction of a PcG pr otein-the Polycomb (PC) protein-with nucleosomal core particles in vitro. T he main nucleosome-binding domain coincides with a region in the C-terminal part of PC previously identified as the repression domain. Our results sug gest that PC, by binding to the core particle, recruits other PcG proteins to chromatin. This interaction could provide a key step in the establishmen t or regulation of higher-order chromatin structures.