5NKL:
reference: Structural Basis for Expansion of the Genetic Alphabet with an Artificial Nucleobase Pair., Betz K, Kimoto M, Diederichs K, Hirao I, Marx A, Angew Chem Int Ed Engl. 2017 Sep 18;56(39):12000-12003. doi:, 10.1002/anie.201704190. Epub 2017 Jun 27. PMID: 28594080

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