5HC9:
reference: Mechanism of 3'-Matured tRNA Discrimination from 3'-Immature tRNA by Class-II CCA-Adding Enzyme., Yamashita S, Tomita K, Structure. 2016 Jun 7;24(6):918-25. doi: 10.1016/j.str.2016.03.022. Epub 2016 Apr, 28. PMID: 27133023

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).