2Z2U:
reference: Crystal Structure of the Radical SAM Enzyme Catalyzing Tricyclic Modified Base Formation in tRNA., Suzuki Y, Noma A, Suzuki T, Senda M, Senda T, Ishitani R, Nureki O, J Mol Biol. 2007 Oct 5;372(5):1204-14. Epub 2007 Jul 26. PMID: 17727881

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