BAH: Owing to extensive intermolecular contacts, the ankyrin repeats of G9a and GLP and the BAH domain of ORC1 show high specificity for di- or monomethylated H3K9 and H4K20me2, respectively. The H3K9me2 peptide is sandwiched between the β-turns and α-helices of the fourth and fifth ankyrin repeats, whereas K9me2 fits into the aromatic cage also containing a glutamate. (1)

Reference
1. Musselman CA, Lalonde ME, Cote J, Kutateladze TG.Perceiving the epigenetic landscape through histone readers. Nat Struct Mol Biol.2012;19(12):1218-27. PMID: 23211769.

    Chromo-Barrel: Chromo-Barrel, as the other member of the Royal family, shows some specificity, preferring tri- or dimethylated H3K36 and monomethylated H4K20 (H4K20me1); however, they bind rather weakly. (1)

Reference
1. Musselman CA, Lalonde ME, Cote J, Kutateladze TG.Perceiving the epigenetic landscape through histone readers. Nat Struct Mol Biol.2012;19(12):1218-27. PMID: 23211769.

    DCD: In the double chromodomain (DCD), both chromodomains share their general secondary structure elements with those previously seen in HP1 and Polycomb chromodomains. The linker segment forms a novel helix–turn–helix structure that juxtaposes the two chromodomains to form a continuous surface. A total of 350 Å is buried at the interface of these tandem chromodomains. (1)

Reference
1. John F. Flanagan, Li-Zhi Mi, Maksymilian Chruszcz, Marcin Cymborowski, Katrina L. Clines, Youngchang Kim, Wladek Minor, Fraydoon Rastinejad & Sepideh Khorasanizadeh.Double chromodomains cooperate to recognize the methylated histone H3 tail. Nature.2005;438:1181–1185. PMID: 16372014.

    PHD: Distinct from the Royal family is the PHD finger, a well-characterized reader of H3K4me3. It contains a C4HC3 motif that coordinates two zinc ions in a cross-brace manner. Such an arrangement produces a globular domain with a small β-sheet and an α-helix. PHD fingers make extensive contacts with H3K4me3, imparting a high degree of specificity. (1)

Reference
1. Musselman CA, Lalonde ME, Cote J, Kutateladze TG.Perceiving the epigenetic landscape through histone readers. Nat Struct Mol Biol.2012;19(12):1218-27. PMID: 23211769.

    TTD: The structurally related TTD module possess a characteristic β-barrel topology and comprise the Royal superfamily. The single Tudor domains of PHF1 and PHF19 have been shown to recognize H3K36me3, whereas the canonical TTD of 53BP1 associates with H4K20me2, and the hybrid TTD of JMJD2A binds H3K4me3 and H4K20me3. (1)

Reference
1. Musselman CA, Lalonde ME, Cote J, Kutateladze TG.Perceiving the epigenetic landscape through histone readers. Nat Struct Mol Biol.2012;19(12):1218-27. PMID: 23211769.