Epigenome programming by Polycomb and Trithorax proteins.

Polycomb group (PcG) and Trithorax group (TrxG) proteins work, respectively, to maintain repressed or active transcription states of developmentally regulated genes through cell division. Data accumulated in the recent years have increased our understanding of the mechanisms by which PcG and TrxG proteins regulate gene expression. The discovery that histone methylation can serve as a specific mark for PcG and TrxG complexes has provided new insight into the mechanistic function of this cell-memory system.