Journal: Nat Commun / Year: 2026 Title: Prokaryotic Schlafen proteins cleave tRNAs during type III CRISPR immunity. Authors: Pedro Weickert / Yang Liu / Jonathan Strecker / Abstract: Schlafen nucleases restrict viral infection in mammals by cleaving self RNAs, however, their function and mechanism in prokaryotic immunity is unknown. Here, we uncover CRISPR-associated Schlafen ...Schlafen nucleases restrict viral infection in mammals by cleaving self RNAs, however, their function and mechanism in prokaryotic immunity is unknown. Here, we uncover CRISPR-associated Schlafen (Cash) proteins containing a Schlafen domain fused to Csx15, an uncharacterized member of Rossmann-like nucleotide-binding sensors. Cash is activated by cyclic tetra-adenylate (cA₄) produced during type III CRISPR interference and induces cell toxicity by cleaving tRNAs, primarily in the T-loop. Cryo-electron microscopy structures of Chloroflexi bacterium Cash reveal an inactive dodecamer, the formation of a filament upon cA₄ binding to align catalytic interfaces, and the molecular basis of substrate recognition and cleavage in a tRNA-bound complex. We identify numerous families of prokaryotic Schlafen proteins associated with diverse antiviral defense systems and characterized by unique sensor domains. This work highlights tRNA depletion by Schlafen nucleases as an evolutionary recurring antiviral strategy and reveals mechanistic differences between Cash and human Schlafen members.
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Conc.: 2 mg/ml / Embedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES Details: CbCash proteins incubated with tRNA Leu at 2:1 ratio, and add cA4 at 100uM before pluging.
Instrument: FEI VITROBOT MARK IV / Cryogen name: ETHANE / Humidity: 100 % / Chamber temperature: 277.15 K / Details: Blot Force 15 Wait Time 0s Blot Time 3.5s
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Electron microscopy imaging
Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company
Microscopy
Model: TFS KRIOS
Electron gun
Electron source: FIELD EMISSION GUN / Accelerating voltage: 300 kV / Illumination mode: FLOOD BEAM
Electron lens
Mode: BRIGHT FIELD / Nominal magnification: 130000 X / Nominal defocus max: 2500 nm / Nominal defocus min: 500 nm / Cs: 2.7 mm / C2 aperture diameter: 100 µm
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