IUBMB Enzyme Nomenclature


Accepted name: ribonuclease T1

Reaction: [RNA] containing guanosine + H2O = an [RNA fragment]-3'-guanosine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA fragment] (overall reaction)
(1a) [RNA] containing guanosine = [RNA fragment]-3'-guanosine-2',3'-cyclophosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA fragment]
(1b) [RNA fragment]-3'-guanosine-2',3'-cyclophosphate + H2O = [RNA fragment]-3'-guanosine-3'-phosphate

Other name(s): barnase; bacterial ribonuclease Sa; guanyloribonuclease; Aspergillus oryzae ribonuclease; RNase N1; RNase N2; ribonuclease N3; ribonuclease U1; ribonuclease F1; ribonuclease Ch; ribonuclease PP1; ribonuclease SA; RNase F1; ribonuclease C2; binase; RNase Sa; guanyl-specific RNase; RNase G; RNase T1; ribonuclease guaninenucleotido-2'-transferase (cyclizing); ribonuclease N1

Systematic name: [RNA]-guanosine 5'-hydroxy-ribonucleotide-3'-[RNA fragment]-lyase (cyclicizing; [RNA fragment]-3'-guanosine-2',3'-cyclophosphate-forming and hydrolysing)

Comments: A family of related enzymes found in some fungi and bacteria. The enzyme is specific for cleavage at the 3'-phosphate group of guanosine in single stranded RNA, and catalyses a two-stage endonucleolytic cleavage. The first reaction produces 5'-hydroxy-phosphooligonucletides and 3'-phosphooligonucleotides ending in Gp with 2',3'-cyclic phosphodiester, which are released from the enzyme. The enzyme then hydrolyses these cyclic compounds in a second reaction that takes place only when all the susceptible 3',5'-phosphodiester bonds have been cyclised. The second reaction is a reversal of the first reaction using the hydroxyl group of water instead of the 5'-hydroxyl group of ribose. The overall process is that of a phosphorus-oxygen lyase followed by hydrolysis to form the 3'-nucleotides.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number:


1. Takahashi, K. The structure and function of ribonuclease T1. I. Chromatographic purification and properties of ribonuclease T1. J. Biochem. (Tokyo) 49 (1961) 1-8.

2. Kasai, K., Uchida, T., Egami, F., Yoshida, K. and Nomoto, M. Purification and crystallization of ribonuclease N1 from Neurospora crassa. J. Biochem. (Tokyo) 66 (1969) 389-396. [PMID: 5348588]

3. Loverix, S., Laus, G., Martins, J.C., Wyns, L. and Steyaert, J. Reconsidering the energetics of ribonuclease catalysed RNA hydrolysis. Eur. J. Biochem. 257 (1998) 286-290. [PMID: 9799130]

[EC created 1961 as EC, transferred 1965 to EC, reinstated 1972 as EC, transferred 1978 to EC, transferred 2020 to EC]

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