In plant and metazoan, Polycomb Group (PcG) proteins play key roles in regulating developmental processes by repression of gene expression. PcG proteins function as multi-protein complexes; among them the best characterized ones are Polycomb Repressive Complex 1 (PRC1) and PRC2. PRC2 catalyzes histone H3 lysine 27 trimethylation (H3K27me3), and PRC1 can bind H3K27me3 and catalyzes H2A monoubiquitination. While the PRC2 components and molecular functions are evolutionarily conserved, varied PRC1 complexes are found and they show high divergences between animals and plants. In addition to the core subunits, an exponentially increasing number of PRC1-associated factors have been identified in Arabidopsis thaliana. Recent studies have also unraveled cross-component interactions and intertwined roles of PRC1 and PRC2 in chromatin modulation. In addition, complexities of interactions and functions between PcG and Trithorax Group proteins have been observed. This short review summarizes up current knowledge to provide insight about repressive functional mechanism of PRC1 and its interplay with other factors.

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