ABSTRACT
The production of ribotoxins as potent as a-Sarcin and restrictocin by aspergini raises questions about the ability of the microbes to protect themselves during production. However, in spite of some promising indications, the antitumor activity of the fungal protein toxins was considered to be too limited and the toxicity too great to merit continued investigation. The ribotoxins a-Sarcin, restrictocin, and mitogillin form a specific class of ribosome-inactivating protein (RIP), they differ in structure and mode of action from the plant RIPs. The plant RIPs exist as single chain or double chain; the latter are substantially more potent in vivo since one of the chains is a cell surface binding protein which targets the toxin. However, the fact that ribonucleolytic activity and sequence homology with “typical” ribonucleases can be found associated with proteins that have diverse biological roles related to this activity suggests that such proteins may play specific roles in cell function.
