IUBMB Enzyme Nomenclature


Accepted name: Enterobacter ribonuclease

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

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

Comments: Preference for cleavage at Cp-A bonds. Homopolymers of A, U or G are not hydrolysed. CpG bonds are hydrolysed less well and there is no detectable hydrolysis between two purines or two pyrimidines.The enzyme catalyses a two-stage endonucleolytic cleavage. The first reaction produces 5'-hydroxy-phosphooligonucletides and 3'-phosphooligonucleotides ending a 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, CAS registry number:


1. Levy, C.C. and Goldman, P. Residue specificity of a ribonuclease which hydrolyzes polycytidylic acid. J. Biol. Chem. 245 (1970) 3257-3262. [PMID: 5432809]

2. Marotta, C.A., Levy, C.C., Weissman, S.M. and Varricchio, F. Preferred sites of digestion of a ribonuclease from Enterobacter sp. in the sequence analysis of Bacillus stearothermophilus 5S ribonucleic acid. Biochemistry 12 (1973) 2901-2904. [PMID: 4719125]

[EC, created 1978 as EC, modified 1981, transferred 2018 to]

Return to EC 4.6.1 home page
Return to EC 4.6 home page
Return to EC 4 home page
Return to Enzymes home page
Return to IUBMB Biochemical Nomenclature home page