Fig. 4.

Combinatorial and sequential histone post-translational modifications (PTMs) deposition by Polycomb complexes. This graphical representation illustrates an example of combinatorial action of histone PTM writers, which add covalent PTMs to histone tails; readers, which recognize and bind histone PTMs; and erasers, which remove histone PTMs. Protein families associated with these steps are listed on the left. In this example, the PRC2 complex adds (writes) trimethylation on lysine 27 of histone H3. This is then recognized by the (reader) complex PRC1. The RING1A and RING1B subunits of PRC1 (writers) subsequently act to ubiquitinate lysine 199 of histone H2A. UTX-1 and JMJD3 can act to remove (erase) histone H3 K27 trimethylation. HMT = histone methyltransferase; HAT = histone acetyl transferase; ADP = adenosine diphosphate; SH2 = Src homology 2; FHA = forkhead-associated; HDMT = histone demethylase; HDAC = histone deacetylase; Me = methylation; Ub = ubiquitination