RNA cyclases are a family of RNA-modifying enzymes that are conserved in all cellular organisms. They catalyze the ATP-dependent conversion of the 3'-phosphate to the 2',3'-cyclic phosphodiester at the end of RNA, in a reaction involving formation of the covalent AMP-cyclase intermediate. The structure of RTC demonstrates that RTCs are comprised two domain. The larger domain contains an insert domain of approximately 100 amino acids.
Lu S et al.(2020). "CDD/SPARCLE: the conserved domain database in 2020.",