223D:
reference: Direct observation of two base-pairing modes of a cytosine-thymine analogue with guanine in a DNA Z-form duplex: significance for base analogue mutagenesis., Moore MH, Van Meervelt L, Salisbury SA, Lin PK, Brown DM, J Mol Biol 1995 Sep 1;251(5):665-73. PMID: 7666418

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