InterPro domain: IPR000228

RNA cyclases are a family of RNA-modifying enzymes that are conserved in eukaryotes, bacteria and archaea. Type 1 RNA 3'-terminal phosphate cyclases ( 6.5.1.4 ) [ 1 , 2 ] catalyse the conversion of 3'-phosphate to a 2',3'-cyclic phosphodiester at the end of RNA:

ATP + RNA 3'-terminal-phosphate = AMP + diphosphate + RNA terminal-2',3'-cyclic-phosphate

The physiological function of the cyclase is not known, but the enzyme could be involved in the maintenance of cyclic ends in tRNA splicing intermediates or in the cyclisation of the 3' end of U6 snRNA [ 3 ].

A second subfamily of RNA 3'-terminal phosphate cyclases (type 2) that do not have cyclase activity have been identified in eukaryotes. They are localised to the nucleolus and are involved in ribosomal modification [ 3 ].

1. The human RNA 3'-terminal phosphate cyclase is a member of a new family of proteins conserved in Eucarya, Bacteria and Archaea. EMBO J. 16, 2955-67
2. RNA 3'-terminal phosphate cyclase from HeLa cells. Meth. Enzymol. 181, 499-510
3. Rcl1p, the yeast protein similar to the RNA 3'-phosphate cyclase, associates with U3 snoRNP and is required for 18S rRNA biogenesis. EMBO J. 19, 2115-26