Wikipedia
Alpha-Sarcin
Alpha-Sarcin is a ribosome-inactivating protein produced in the mold Aspergillus giganteus. Specifically, alpha-sarcin cleaves the a portion of ribosomal RNA that forms the small ribosomal substrate. The high specificity of alpha-sarcin and its efficiency of cleavage are point of study and also account for this protein's very high toxicity level.