ID   4.6.1.20
DE   ribonuclease U2.
AN   RNase U2.
CA   (1) [RNA] containing adenosine + H2O = an [RNA fragment]-3'-adenosine-
CA   3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA fragment].
CA   (2) [RNA] containing guanosine + H2O = an [RNA fragment]-3'-guanosine-
CA   3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA fragment].
CC   -!- The enzyme secreted by the fungus Ustilago sphaerogena cleaves at the
CC       3'-phosphate group of purines, and catalyzes a two-stage
CC       endonucleolytic cleavage.
CC   -!- The first reaction produces 5'-hydroxy-phosphooligonucletides and
CC       3'-phosphooligonucleotides ending in Ap or Gp with 2',3'-cyclic
CC       phosphodiester, which are released from the enzyme.
CC   -!- The enzyme then hydrolyzes these cyclic compounds in a second
CC       reaction that takes place only when all the susceptible
CC       3',5'-phosphodiester bonds have been cyclised.
CC   -!- The second reaction is a reversal of the first reaction using the
CC       hydroxyl group of water instead of the 5'-hydroxyl group of ribose.
CC   -!- The overall process is that of a phosphorus-oxygen lyase followed by
CC       hydrolysis to form the 3'-nucleotides.
CC   -!- Formerly EC 3.1.27.4.
DR   P00654, RNU2_USTSP ;
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