EZH2 (UniProt/Swiss-Prot entry Q15910) is a histone-lysine methyltransferase which methylates ‘Lys-9’ and ‘Lys-27’ of histone H3, leading to transcriptional repression. It is a member of the polycomb group (PcG) family which form multimeric protein complexes and are involved in maintaining the transcriptional repressive state of genes over successive cell generations. The EZH2 activity is dependent on the association with other components of the PRC2 complex (EED, SUZ12/JJAZ1, RBBP4 and RBBP7). EZH2 may play a role in the hematopoietic and central nervous systems. Over-expression of EZH2 is observed during advanced stages of prostate cancer and breast cancer.