DarHTG is a tripartite phage defence system for purine DNA base ADP-ribosylation

DarHTG is a tripartite bacterial phage defence system that enables ARH-family ADP-ribosylation of double-stranded DNA, expanding targets to adenosine and guanosine bases.

• Why it matters: Phages constantly threaten bacteria, and known DarTG toxin-antitoxin defences mainly target single-stranded DNA, leaving double-stranded DNA mechanisms unclear.
• What they did: The authors characterize DarHTG across bacteria, defining two subclasses that use DarT plus a non-processive superfamily I helicase as a co-toxin, and identify ARH antitoxins that reverse adenosine or guanosine modifications.
• The result: DarHTG provides resistance to a broad range of bacteriophages and is triggered by highly charged tails of viral single-stranded DNA-binding proteins that occlude the ARH antitoxin active site.

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