EC - Ribonuclease U2

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IntEnz Enzyme Nomenclature


Accepted name:
ribonuclease U2
Other names:
Pleospora RNase
Trichoderma koningi RNase III
RNase U2
RNase U3
purine specific endoribonuclease
purine-specific RNase
purine-specific ribonuclease
ribonuclease (purine)
ribonuclease U3
ribonuclease U2
Systematic name:
[RNA]-purine 5'-hydroxy-ribonucleotide-3'-[RNA fragment]-lyase (cyclicizing; [RNA fragment]-3'-purine-nucleoside -2',3'-cyclophosphate-forming and hydrolysing)



The enzyme secreted by the fungus Ustilago sphaerogena cleaves at the 3'-phosphate group of purines, and catalyses a two-stage endonucleolytic cleavage. The first reaction produces 5'-hydroxy-phosphooligonucletides and 3'-phosphooligonucleotides ending in Ap or 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. Formerly EC

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0033899


  1. Glitz, D.G. and Dekker, C.A.
    Studies on a ribonuclease from Ustilago sphaerogena. I. Purification and properties of the enzyme.
    Biochemistry 3 : 1391-1399 (1964). [PMID: 14230791]
  2. Glitz, D.G. and Dekker, C.A.
    Studies on a ribonuclease from Ustilago sphaerogena. II. Specificity of the enzyme.
    Biochemistry 3 : 1399-1406 (1964). [PMID: 14230792]
  3. Uchida, T. and Egami, F.
    Microbial ribonucleases with special reference to RNases T1, T2, N1, and U2.
    In: Boyer, P.D. (Ed.) The Enzymes , 3rd ed. vol. 4 , Academic Press , New York , 1971 , 205-250
  4. Martinez-Ruiz, A., Garcia-Ortega, L., Kao, R., Onaderra, M., Mancheno, J. M., Davies, J., Martinez del Pozo, A., Gavilanes, J. G.
    Ribonuclease U2: cloning, production in Pichia pastoris and affinity chromatography purification of the active recombinant protein.
    FEMS Microbiol. Lett. 189 : 165-169 (2000). [PMID: 10930732]

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