Prokaryotic Immunity and Viral Evasion Systems

The defense-associated sirtuin 2 (DSR2) effector protects bacteria from phage infection by depleting NAD⁺. Here, the authors employ biochemical and structural approaches to reveal the inhibition and activation mechanisms of DSR2 by the phage anti-DSR2 protein (DSAD1) and tail tube protein (TTP).

Short prokaryotic Argonaute and Sir2 proteins function as an antivirus system. Here the authors describe structures of SPARSA (a heterodimer of Sir2-APAZ and prokaryotic Argonaute) with and without template DNA and guide RNA, providing structural basis of its assembly and activation by the recognition of the invading virus.

Utilising AcrIIC1, which can provide an ‘off-switch’ by inhibiting the DNA cleavage activity of ThermoCas9 and GeoCas9, a Class 2 CRISPR-Acr tool is described for gene silencing and base-editing applications.

Bacteria and archaea have developed multiple antiviral mechanisms. Here, Tesson et al. present a tool that automatically detects known antiviral systems in prokaryotic genomes, and show that variations in antiviral strategies correlate with genome size, viral threat, and lifestyle traits.