RNA Polymerase Backtracking Promotes Type III-A CRISPR DNA Targeting

GreA anti-backtracking activity selectively suppresses Cas10-Csm DNA targeting in type III CRISPR immunity, and GreA overexpression abolishes protection against both phages and conjugative plasmids.

• Why it matters: Type III CRISPR targets DNA in a transcription-dependent way, but how RNA polymerase behavior creates the DNA substrates for Cas10-Csm remained unclear.
• What they did: The study tested GreA overexpression and GreA anti-backtracking–disrupting mutations for effects on type III versus type II immunity, including comparisons with Csm6-mediated responses.
• The result: GreA specifically inhibits Cas10-dependent DNA interference, while type II CRISPR-Cas immunity and Csm6 remain unaffected, supporting a model where arrested transcription complexes enable DNA degradation.

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