The Acidic Ribosomal Stalk Proteins Are Not Required for the Highly Specific Inactivation Exerted by α-Sarcin of the Eukaryotic Ribosome

The ribosomal sarcin/ricin loop (SRL) is the target of ribosome-inactivating proteins like the N-glycosidase ricin and the fungal ribotoxin alpha-sarcin. The eukaryotic ribosomal stalk directly interacts with several members of the N-glycosidase family, favoring their disruption of the SRL. Here we tested this hypothesis for the ribotoxin alpha-sarcin. Experiments with isolated ribosomes, cell-free translation systems, and viability assays with Saccharomyces cerevisiae strains defective in acidic stalk proteins showed that the inactivation exerted by alpha-sarcin is independent of the composition of the ribosomal stalk. Therefore, alpha-sarcin, with the same ribosomal target as ricin, seems to access the SRL by a different pathway.