The Enzyme Database

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EC 4.6.1.21     
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, PDB, CAS registry number: 395640-99-0
References:
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 4.6.1.21 created 1978 as EC 3.1.27.6, modified 1981, transferred 2018 to 4.6.1.21]
 
 


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