Abstract
Polycomb group (PcG) proteins are important for maintaining the silenced state of homeotic genes. Biochemical and genetic studies in Drosophila and mammalian cells indicate that PcG proteins function in at least two distinct protein complexes: the ESC-E(Z) or EED-EZH2 complex, and the PRC1 complex. Recent work has shown that at least part of the silencing function of the ESC-E(Z) complex is mediated by its intrinsic activity for methylating histone H3 on lysine 27. In addition to being involved in Hox gene silencing, the complex and its associated histone methyltransferase activity are important in other biological processes including X-inactivation, germline development, stem cell pluripotency and cancer metastasis.
