Noncanonical PRC1.1 complex and canonical PRC2 and PCR1 complexes in HSCs. The BCOR complex is recruited to the chromatin via binding of KDM2B to nonmethylated CpG islands, and it catalyzes the ubiquitination of the histone H2A at Lys119 (H2AK119ub) via the RING-PCGF1 enzymatic core. Ubiquinated loci (white asterisk) recruit the histone methyltransferase EZH2, one of the components of the polycomb repressor complex 2 (PRC2). PRC2 is then responsible for the histone H3 methylation at Lys27 (H3K27me3). All these histone modifications lead to the suppression of gene transcription. Canonical PRC1 complex through its components RING1B and CBX catalyzes both the ubiquitination of the histone H2A at Lys119 (H2AK119ub) and the histone H3 methylation at Lys27 (H3K27me3), also leading to the suppression of gene transcription.