4ISZ:
reference: Structures of the Noncanonical RNA Ligase RtcB Reveal the Mechanism of Histidine Guanylylation., Desai KK, Bingman CA, Phillips GN Jr, Raines RT, Biochemistry. 2013 Apr 16;52(15):2518-25. doi: 10.1021/bi4002375. Epub 2013 Apr, 5. PMID: 23560983

This OCA Structure page
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