The Pseudomonas aeruginosa ribonuclease Ribocin cleaves eukaryotic ribosomes at helix 69 to inhibit host translation.

Pseudomonas aeruginosa employs host translation inhibition as a virulence-enhancing strategy. We previously showed that the bacterium induces cleavage of Caenorhabditis elegans large ribosomal RNA at helix 69 (H69), part of a central intersubunit bridge and the ribosomal decoding center. In this study, we demonstrate that a previously uncharacterized ribonuclease, Ribocin, is necessary and sufficient for H69 cleavage. Recombinant Ribocin cuts H69 in worm and mammalian ribosomes, indicating that H69 cleavage by P. aeruginosa is phylogenetically conserved. In worms, mammalian cells, and rabbit reticulocyte lysates, H69 cleavage results in translation inhibition. Furthermore, Ribocin contributes to bacterial virulence toward C. elegans, triggers a major host response to translation inhibition, and operates in parallel with Exotoxin A-mediated translation inhibition. These findings unveil the first known nuclease that cleaves eukaryotic ribosomes at H69 and expand the understanding of host translation-inhibition by establishing targeted rRNA cleavage as a mechanism of host attack.