NatureJul 22, 2026

CRISPR-Cas controls activity of built-in anti-virus defense systems

CRISPR Gene Editing Weekly Brief ↗PubMed ↗DOI ↗

Updated Jul 23, 2026

Abstract

CRISIS (CRISPR-supervised immune system) embeds and regulates diverse innate defence mechanisms in bacteria.

Type I CRISPR-Cas loci can transcriptionally modulate various immune cassettes for antiviral defence.
Small RNA-like molecules guide the Cascade effector complex to inhibit promoters of these immune systems.
This regulation allows for basal expression of immune responses while reducing potential negative impacts on host growth.
When CRISPR-Cas systems face mutations or anti-CRISPR proteins, transcription of defence systems increases significantly.
Enhanced transcription leads to stronger innate immunity but may compromise host fitness.

Simplified

Bacteria utilize diverse defence systems to protect against harmful foreign DNA such as bacteriophages^1,2, but how these systems coordinate with each other remains poorly understood. Here we uncover CRISIS (CRISPR-supervised immune system), a widespread regulatory paradigm whereby type I CRISPR-Cas loci embed and transcriptionally modulate diverse innate defences. Small non-canonical CRISPR RNA (crRNA)-like RNAs guide the I-C CRISPR-associated complex for antiviral defence (Cascade) effector complex to inhibit promoters of diverse immune cassettes-including composite multi-system clusters-enabling their basal expression for antiviral activity while mitigating fitness costs associated with hyperactivation, such as host growth impairment or exclusion of beneficial plasmids. When CRISPR-Cas is compromised by mutation or anti-CRISPR proteins, there is a burst in transcription of these embedded defence systems, leading to higher-level innate immunity at the expense of host fitness. Together, adaptive CRISPR-Cas systems orchestrate diverse innate immune systems into a layered defence network, comprising a prokaryotic 'immunity guard' strategy.

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CRISPR-Cas controls activity of built-in anti-virus defense systems

Abstract

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