Updated project metadata. Circadian rhythmicity of gene expression is a conserved feature of cell physiology. This involves fine tuning between transcriptional and post-transcriptional molecular mechanisms, strongly dependent on the metabolic state of the cell, which guarantees adaptive plasticity of tissue-specific genetic programs. Dynamics of epigenome structure and epigenetic regulators support this plasticity. However, the intermingle between epigenome and RNA Pol II rhythmicity remains to be investigated. Here we identify the Polycomb group (PcG) protein EZH1 as a gateway bridging function regulating periodic alternation between chromatin mediated silencing and active transcription in post-mitotic skeletal muscle cells. We show that PRC2-EZH1 core components are under direct regulation of BMAL1, and show an oscillatory behavior and a regulated periodic assembly of PRC2-EZH1 complex. Instead at alternate Zeitgeber points, EZH1 becomes essential for circadian gene expression, through stabilization of RNA Pol II preinitiation complex controlling nascent transcription process. Collectively, our data show that EZH1 depending on the stoichiometry of its partners guarantees both negative and positive modulation of RNA Pol II activity, resulting in oscillatory transcription.