Bacteriophages suppress CRISPR-Cas immunity using RNA-based anti-CRISPRs

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacteria utilize CRISPR-Cas systems for adaptive immunity against mobile genetic elements like phages and plasmids.
• Mobile genetic elements have evolved anti-CRISPR proteins to evade bacterial immune responses.

Purpose of the Study:

• To investigate a novel class of anti-CRISPR mechanisms based on small non-coding RNAs.
• To characterize the function and prevalence of RNA-based anti-CRISPR strategies.

Main Methods:

• Identification of small non-coding RNA anti-CRISPRs (Racrs) in viral genomes.
• Experimental validation of Racr function against the type I-F CRISPR-Cas system.
• Inhibition assays and analysis of Cas subcomplex formation.

Main Results:

• Racrs, encoded as solitary repeat units in viral genomes, mimic CRISPR array repeats.
• A prophage-encoded Racr specifically inhibits the type I-F CRISPR-Cas system by forming aberrant Cas6f-Cas7f complexes.
• Nine tested Racr candidates across two CRISPR-Cas classes demonstrated potent immune inhibition.

Conclusions:

• Molecular mimicry of CRISPR repeats represents a widespread anti-CRISPR strategy employed by viruses.
• This discovery opens avenues for biotechnological applications in gene editing and synthetic biology.