6CHG:
reference: Crystal Structure of the COMPASS H3K4 Methyltransferase Catalytic Module., Hsu PL, Li H, Lau HT, Leonen C, Dhall A, Ong SE, Chatterjee C, Zheng N, Cell. 2018 Aug 23;174(5):1106-1116.e9. doi: 10.1016/j.cell.2018.06.038. Epub 2018, Aug 9. PMID: 30100181

This OCA Structure page
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