question: Which histone modifications are associated with Polycomb group (PcG) proteins?
answer: A member of the polycomb repressive complex 2 (PRC2) directly mediates the addition of K27me3 to histone H3, a modification associated with heterochromatin, and it is believed that this activity mediates transcriptional repression. At the same time PRC2 activity results in a global increase in H3K27 acetylation. Some members of the PcG display affinity towards both histone H3 trimethylated at K9 and H3K27me3, and one CD prefers K9me3.