PRC2 (polycomb repressive complex 2) is one of the two classes of polycomb-group proteins or (PcG). 

The other component of this group of proteins is PRC1 (Polycomb Repressive Complex 1).

The PRC2 complex has histone methyltransferase activity and primarily methylates histone H3 on lysine 27 a mark of transcriptionally silent chromatin. 

PRC2 is required for initial targeting of genomic region to be silenced, while PRC1 is required for stabilizing this silencing and underlies cellular memory of silenced region after cellular differentiation. 

These proteins are required for epigenetic silencing of chromatin and have an important role in stem cell differentiation and early embryonic development. 

PRC2 has a role in X chromosome inactivation, in maintenance of stem cell fate, and in imprinting. 

Aberrant expression of PRC2 has been observed in cancer.

Polycomb group genes directly and indirectly regulate the DNA damage response which acts as an anti-cancer barrier.

The PRC2 complex appears to be present at sites of DNA double-strand breaks where it promotes repair of such breaks by non-homologous end joining.

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