This purine-specific ribonuclease cleaves 28S RNA in eukaryotic ribosomes, inhibits protein synthesis, and shows antitumor activity. Causes an allergic reaction in human. Binds to IgE. May promote colonization through cytotoxic activity and by causing inflammatory reactions involving IgE antibodies. Binds also to IgG. Belongs to the ribonuclease U2 family.