Dear Editor,
The highly conserved polycomb group (PcG) proteins were initially identified in Drosophila to maintain repression state of the transcription of homeotic genes, which is critical for animal development control (Sawarkar and Paro, 2010). Polycomb repressive complexes 1 (PRC1) and 2 (PRC2) are two important multi-protein complexes of PcG proteins regulating target gene expression. In Drosophila, PRC2 is composed of Enhancer of zeste (E(z)), Suppressor of zeste 12 (Su(z)12), Extra sex combs (esc), and Chromatin assembly factor 1 subunit (Caf1). E(z) is the catalytic subunit for H3K27me2/3, while both Su(z)12 and Esc are...