Genome binding/occupancy profiling by high throughput sequencing Expression profiling by high throughput sequencing
Polycomb Repressive Complexes (PRC), and their chromatin-modifying activities, are essential for the correct regulation of gene expression during cellular differentiation and development. Although their role in transcriptional repression is well described, a detailed molecular understanding of their complex assembly and enzymatic activity has been lacking. We therefore set out to characterize the relationship between PRC1 complex composition and its ability to catalyse H2AK119ub1 for one of the most abundant PRC1 complexes in embryonic stem cells, PCGF1-PRC1. Biochemical reconstitution of the PCGF1-PRC1 complex revealed that RYBP/YAF2 was essential for robust enzymatic activity of the complex. Using calibrated ChIP-seq for H2AK119ub1, we identify that RYBP-dependent PRC1 activity has a widespread role in shaping H2AK119ub1 levels genome-wide in mouse embryonic stem cells. Furthermore, these H2AK119ub1 levels stimulate PRC2 activity as part of an activity-based feedback loop, which we demonstrate is required for maintenance of transcriptional repression. Together, these observations uncover complex-based principles for PRC1 assembly and activity, and further our understanding of Polycomb domain function.
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