2FHD:
reference: Structural basis for the methylation state-specific recognition of histone H4-K20 by 53BP1 and Crb2 in DNA repair., Botuyan MV, Lee J, Ward IM, Kim JE, Thompson JR, Chen J, Mer G, Cell. 2006 Dec 29;127(7):1361-73. PMID: 17190600

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