Catalyzes the conversion of 3'-phosphate to a 2',3'-cyclic phosphodiester at the end of RNA (PubMed:9184239). The mechanism of action of the enzyme occurs in 3 steps: (A) adenylation of the enzyme by ATP; (B) transfer of adenylate to an RNA-N3'P to produce RNA- N3'PP5'A; (C) and attack of the adjacent 2'-hydroxyl on the 3'- phosphorus in the diester linkage to produce the cyclic end product (PubMed:9184239). Likely functions in some aspects of cellular RNA processing (PubMed:25961792, PubMed:9184239). Function plays an important role in regulating axon regeneration by inhibiting central nervous system (CNS) axon regeneration following optic nerve injury (PubMed:25961792). {ECO:0000269|PubMed:25961792, ECO:0000269|PubMed:9184239}. This is the function of Ensembl gene identifier ENSG00000137996 (RTCA, RNA 3'-terminal phosphate cyclase).