5C7U:
reference: A Crystal Structure of a Functional RNA Molecule Containing an Artificial Nucleobase Pair., Hernandez AR, Shao Y, Hoshika S, Yang Z, Shelke SA, Herrou J, Kim HJ, Kim MJ, Piccirilli JA, Benner SA, Angew Chem Int Ed Engl. 2015 Aug 17;54(34):9853-6. doi: 10.1002/anie.201504731., Epub 2015 Jul 16. PMID: 26223188

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