Enhancer of zeste homolog 2 (Ezh2) is a member of the Polycomb group (PcG). The PcG proteins are involved in maintaining the silenced state of several developmentally regulated genes and contribute to the maintenance of cell identity, cell cycle regulation, and oncogenesis. Enhancer of zeste homolog 2 (Ezh2) contains four conserved regions including domain I, domain II, and a cysteine-rich amino acid stretch that precedes the carboxy-terminal SET domain. Ezh2 also plays a role as primary effector and as a mediator of tumorigenesis.