{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T14:48:40Z","timestamp":1791902920750,"version":"4.3.4"},"posted":{"date-parts":[[2026,10,9]]},"group-title":"Microbiology","reference-count":43,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2026,10,9]],"date-time":"2026-10-09T00:00:00Z","timestamp":1791504000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"id":[{"id":"https:\/\/ror.org\/006w34k90","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,10,9]]},"abstract":"<jats:p>Bacterial small-molecule messengers that function in diverse immune signaling pathways have been thought to derive strictly from biosynthesis using nucleotide and cofactor substrates. Here we report a nuclease-driven immune signaling pathway in which tRNA cleavage generates a specific small molecule that triggers cell death in response to RNA-guided transcript recognition in prokaryotes. We identify a class of type VI-B CRISPR systems in which the RNA-guided nuclease Cas13 and its accessory transmembrane protein, 2TM\u03b2, are co-encoded in an operon and are jointly required for bacteriophage defense. Upon target RNA recognition, Cas13 activates 2TM\u03b2 by producing mono- and dinucleotide messengers bearing 2\u2032,3\u2032-cyclic uridine phosphate ends by tRNA cleavage. Activated 2TM\u03b2 destroys infected cells by forming a multimeric complex that disrupts cell membranes to mediate cell death. 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