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ENZYME entry: EC

Accepted Name
Alternative Name(s)
rRNA endonuclease
Reaction catalysed
a 28S rRNA containing guanosine-adenosine pair + H2O <=> an [RNA fragment]-3'-adenosine-3'-phosphate + a 5'-a hydroxy-guanosine-3'-[RNA fragment]
  • Ribotoxins are rRNA endonucleases that catalyze the cleavage of the phosphodiester bond between guanosine and adenosine residues at one specific position in 28S rRNA.
  • The enzyme secreted by Aspergillus giganteus specifically cleaves rat 28S rRNA between G(4325) and A(4326) and displays cytotoxic activity toward animal cells.
  • It can also act on bacterial rRNAs.
  • The enzyme catalyzes a two-stage endonucleolytic cleavage.
  • The first reaction produces 5'-hydroxy-phosphooligonucletides and 3'-phosphooligonucleotides ending with 2',3'-cyclic phosphodiester, which are released from the enzyme.
  • The enzyme then hydrolyzes 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
PRIAM enzyme-specific profiles4.6.1.23
KEGG Ligand Database for Enzyme Nomenclature4.6.1.23
IUBMB Enzyme Nomenclature4.6.1.23
MEDLINEFind literature relating to
Rhea expert-curated reactions4.6.1.23

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