Helicase family proteins promote antiviral ADP-ribosylation of DNA purines

The Escherichia coli DarHTG3 defense system promotes broad phage protection by requiring DarH and ADP-ribosylating adenine on DNA purines.

• Why it matters: DarTG systems use toxin–antitoxin pairs to block phage replication, but additional subfamilies and how helicase proteins regulate the antiviral modification were unclear.
• What they did: The study identified a DarT3 toxin with an ARH-domain antitoxin and a helicase-family protein DarH, then characterized DarH-containing DarTG systems to map whether targets include adenine or guanine.
• The result: Data support a model where ADP-bound DarH acts as a processivity factor that recruits DarT to single-stranded DNA, enabling multiple ADP-ribosylation sites and expanding helicase-family roles in bacterial immunity.

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