In this project, we provide strong proteomic evidence for PcG interaction with classic co-activators, BRD4 and MOZ/MORF, captured on chromatin during embryogenesis in Drosophila, leading to a model in which developmental regulatory elements are universally ‘poised’ early in development via occupancy of composite protein complexes of PcG silencing proteins and classical co-activators. These bivalent protein interactions may resolve into full activation or repression, depending on the cell type-specific expression, binding, and function of transcription factors.