EC Explorer

4.6.1.20

ribonuclease U₂

(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

purine specific endoribonuclease, ribonuclease U₃, RNase U₃, RNase U₂, purine-specific ribonuclease, purine-specific RNase, Pleospora RNase, Trichoderma koningi RNase III, ribonuclease (purine)

[RNA]-purine 5′-hydroxy-ribonucleotide-3′-[RNA fragment]-lyase (cyclicizing; [RNA fragment]-3′-purine-nucleoside -2′,3′-cyclophosphate-forming and hydrolysing)

37205-57-5

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.

created 1978 as 3.1.27.4, modified 1981, transferred 2018 to EC 4.6.1.20