3VRH:
reference: Crystallographic and mutational studies on the tRNA thiouridine synthetase TtuA., Nakagawa H, Kuratani M, Goto-Ito S, Ito T, Katsura K, Terada T, Shirouzu M, Sekine SI, Shigi N, Yokoyama S, Proteins. 2013 Feb 27. doi: 10.1002/prot.24273. PMID: 23444054

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