Quality control system that monitors ribosomes damaged by verotoxin

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Verotoxin is produced by enterohemorrhagic E. coli. It targets a small domain called SRL (Sarcin-Ricin Loop) in the host ribosomal RNA. The target site of this toxin was precisely determined; however, the consequence of this damage, including the effect on the ribosomal function and the cellular stress-response systems, has not been explored extensively. In this research, we tackled this problem using S. cerevisiae system as a model. We revealed that 25S rRNA with a mutation in SRL is nonfunctional and selectively degraded in vivo. From 5000 mutant strains of the yeast knock-out collection, we identified several strains that accumulate the SRL mutant 25S rRNA. Interestingly, the genes involved in the degradation of the SRL mutant are partially overlapped with those involved in 25S NRD (degradation pathway for another type of nonfunctional 25S rRNA). These results suggest a general quality control mechanism that monitors a wealth of defects caused by a number of reasons.