Figure 1.

The modular composition of the epigenetic machinery. (A) Venn diagram illustrating the three broad categories of the epigenetic machinery (histone machinery, DNA methylation machinery, and remodelers), their relative sizes, and their mutual relationships. (B) Venn diagram illustrating the four broad “action” categories of the machinery (writers, erasers, remodelers, and readers), their relative sizes, and their mutual relationships. The modularity of this organization is evident, with some reader components exhibiting enzymatic functions and/or more than one reading function. In contrast, the individual enzymatic component types are pairwise mutually exclusive.