Figure 5. Polycomb repressive complex (PRC)-1 and PRC-2 work cooperatively.

Enhancer of zeste homolog 2 (EZH2), the catalytic subunit of PRC-2 with methyltransferase activity, mediates the covalent trimethylation of histone H3 at lysine 27 (H3K27me3). This specific histone modification serves as the docking site for proteins harboring a chromobox domain (especially Cbx4 and Cbx8) that aid in the recruitment of PRC-1 to chromatin through their interactions with H3K27me3. Thereafter, PRC-1 catalyzes the monoubiquitilation of histone H2A at lysine 119 through the enzymatic action of RING1/RING1b and blocks transcriptional elongation by RNA polymerase II.