The Polycomb group--no longer an exclusive club?

Polycomb group (PcG) proteins maintain silencing at target loci in higher eukaryotes but recent evidence suggests that about half of these proteins are also required for maintenance of activation at homeotic loci. We suggest that PcG and trithorax group response elements should acquire a new name, 'maintenance elements', to reflect the dual function of regulatory elements that bind both groups of proteins. New data suggest that there might be a functional link between PcG repression and cell-cycle regulation.