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EC 4.6.1.20 Details
EC number
4.6.1.20
Accepted name
ribonuclease U2
Reaction
(1) [RNA] containing adenosine + H2O = an [RNA fragment]-3′-adenosine-3′-phosphate + a 5′-hydroxy-ribonucleotide-3′-[RNA fragment] (overall reaction);;(1a) [RNA] containing adenosine = an [RNA fragment]-3′-adenosine-2′,3′-cyclophosphate + a 5′-hydroxy-ribonucleotide-3′-[RNA fragment];;(1b) an [RNA fragment]-3′-adenosine-2′,3′-cyclophosphate + H2O = an [RNA fragment]-3′-adenosine -3′-phosphate;;(2) [RNA] containing guanosine + H2O = an [RNA fragment]-3′-guanosine-3′-phosphate + a 5′-hydroxy-ribonucleotide-3′-[RNA fragment] (overall reaction);;(2a) [RNA] containing guanosine = an [RNA fragment]-3′-guanosine-2′,3′-cyclophosphate + a 5′-hydroxy-ribonucleotide-3′-[RNA fragment];;(2b) an [RNA fragment]-3′-guanosine-2′,3′-cyclophosphate + H2O = an [RNA fragment]-3′- guanosine-3′-phosphate
Other name(s)
purine specific endoribonuclease, ribonuclease U3, RNase U3, RNase U2, purine-specific ribonuclease, purine-specific RNase, Pleospora RNase, Trichoderma koningi RNase III, ribonuclease (purine)
Systematic name
[RNA]-purine 5′-hydroxy-ribonucleotide-3′-[RNA fragment]-lyase (cyclicizing; [RNA fragment]-3′-purine-nucleoside -2′,3′-cyclophosphate-forming and hydrolysing)
CAS registry number
37205-57-5
Comment
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.
History
created 1978 as 3.1.27.4, modified 1981, transferred 2018 to EC 4.6.1.20
EC Tree
1.13.11.7 created 1965 as EC 1.13.1.7, transferred 1972 to EC 1.13.11.7, deleted 1980
1.13.11.21 created 1972, deleted 2001