Alpha-sarcin is an extracellular cytotoxic protein produced by the mold Aspergillus giganteus. It is a specific ribonuclease which inhibits protein synthesis by cleaving a specific phosphodiester bond in the highly conserved sarcin-ricin loop of the 28S rRNA. The enzyme is a member of a distinctive family of fungal ribonucleases known as ribotoxins, which are produced by different Aspergillus species. The ribotoxins show high sequence homology to each other and are also related to the RNAse T1 subfamily of microbial ribonucleases.