2XEU:
reference: Mechanism of ubiquitylation by dimeric RING ligase RNF4., Plechanovova A, Jaffray EG, McMahon SA, Johnson KA, Navratilova I, Naismith JH, Hay RT, Nat Struct Mol Biol. 2011 Aug 21;18(9):1052-9. doi: 10.1038/nsmb.2108. PMID: 21857666

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