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bioRxiv · 10.64898/2026.02.22.705581

Viral SSB-bound ssDNA activates the bacterial anti-phage defense system DARNA

Puteikiene, R.·Vassallo, C.·Silanskas, A.·Juozapaitis, J.·Songailiene, I.·Laub, M. T.·Sasnauskas, G.
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Abstract

To protect themselves against phage infection, bacteria employ diverse defense systems that are typically activated specifically upon infection. However, the mechanisms of activation and self versus non-self discrimination for most systems remain poorly understood. Here, we show that the bacterial immunity protein DARNA, once activated, cleaves a subset of host tRNAs, thereby inhibiting phage propagation. Although phages escape DARNA-mediated defense through mutations in the gene encoding single-stranded DNA-binding protein (SSB), we find that phage SSBs do not directly stimulate DARNA. Instead, DARNA is activated by single-stranded DNA presented by phage SSB, but not by the host SSB. The recognition of an endogenous nucleic acid signal promoted by a viral protein ensures that DARNA can detect and respond to a broad range of viruses while avoiding auto-immunity.

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Puteikiene, R., Vassallo, C., Silanskas, A., Juozapaitis, J., Songailiene, I., Laub, M. T., Sasnauskas, G.. 2026-02-23. Viral SSB-bound ssDNA activates the bacterial anti-phage defense system DARNA. https://doi.org/10.64898/2026.02.22.705581

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