Nuclear RIOX1 (Ribosomal oxygenase NO66) 3-hydroxylates histidine 216 of RPL8 (60S ribosomal protein L8) (Ge et al. 2012). The oligomerization state of RIOX1 in vivo is unknown; it is annotated here as a monomer complexed with one Fe2+ ion (Brauer et al. 2018).