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Updated: Sep 9, 2025

Substrate Generation for Endonucleases of CRISPR/Cas Systems
11:53

Substrate Generation for Endonucleases of CRISPR/Cas Systems

Published on: September 8, 2012

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Diversity and abundance of ring nucleases in type III CRISPR-Cas loci

Ville Hoikkala1, Haotian Chi1, Sabine Grüschow1

  • 1School of Biology, University of St Andrews, St Andrews, UK.

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
|September 4, 2025
PubMed

Insights

Type III CRISPR-Cas systems use cyclic oligoadenylates (cOAs) for phage defense. This study confirms new ring nucleases (RNs) that degrade cOAs, revealing widespread regulation of these signaling molecules in bacterial immunity.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genomics

Background:

  • Type III CRISPR-Cas systems provide adaptive immunity against phages by producing cyclic oligoadenylates (cOAs).
  • cOAs activate downstream effectors, but their uncontrolled production can be toxic to cells.
  • Regulation of cOA levels is crucial for bacterial survival during and after infection.

Purpose of the Study:

  • To conduct a comprehensive bioinformatic analysis of type III CRISPR-Cas loci globally.
  • To identify and characterize ring nucleases (RNs) involved in cOA degradation within these systems.
  • To explore the distribution and co-occurrence patterns of RNs and their associated effectors.

Main Methods:

  • Analysis of 38,742 prokaryotic genomes.
  • Bioinformatic identification of known and predicted ring nucleases (RNs) in type III CRISPR loci.
  • Experimental confirmation of Csx16 and Csx20 as active RN enzymes.

Main Results:

  • Identified and confirmed Csx16 and Csx20 as functional ring nucleases, alongside Crn1-3.
  • Revealed widespread distribution and co-occurrence patterns of various RNs within type III CRISPR systems.
  • Demonstrated that a majority of type III CRISPR systems employ RNs to degrade cOA signaling molecules.

Conclusions:

  • A significant proportion of type III CRISPR systems utilize ring nucleases to regulate cyclic oligoadenylate levels.
  • This regulation of cOA degradation is a key factor influencing bacterial cell fate following viral infections.
  • The findings provide a global overview of RNs in type III CRISPR immunity and their ecological implications.
Keywords:
CRISPRcyclic nucleotidephosphodiesterasering nuclease

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