RNA 3'-terminal phosphate cyclases and cyclase-like proteins

RNA molecules bearing terminal 2', 3'-cyclic phosphate are quite common in nature. For example, 2', 3'-cyclic phosphate termini are produced during RNA cleavage by many endoribonucleases either as intermediates or final products. Many RNA-based nucleases (ribozymes) also generate cyclic phosphate termini. However, cleavage reactions are not the only way in which RNAs bearing cyclic phosphate ends are produced. They can also be generated by RNA 3'-terminal phosphate cyclases (RtcA), a family of enzymes conserved in eukaryotes, bacteria, and archaea. These enzymes catalyze the ATP-dependent conversion of the 3'-phosphate to a 2', 3'-cyclic phosphodiester at the end of RNA. In this article, I review knowledge about the biochemistry and structure of RNA 3'-phosphate cyclases and also proteins of the RNA cyclase-like (Rcl1) family, and discuss their documented or possible roles in different RNA metabolic reactions.