A large, distinct family of RNase H fold nucleases associated with numerous defense systems in prokaryotes

WARD proteins, a DUF3800 family with a distinct RNase H fold variant, are encoded in 15% of complete prokaryotic genomes and protect Escherichia coli from phages.

• Why it matters: Prokaryotic immunity surveys revealed hundreds of defense systems, implying many remain uncharacterized; identifying abundant, functional families helps close this gap.
• What they did: The authors performed a genomic census of DUF3800 proteins and analyzed defense-island associations, then experimentally tested 10 WARDs in Escherichia coli for phage protection.
• The result: Nine of 10 tested WARDs conferred robust protection against diverse phages in Escherichia coli, implying WARDs are the third most abundant prokaryotic defense system type.

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