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Substrate Generation for Endonucleases of CRISPR/Cas Systems
Published on: September 8, 2012
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Integrase-mediated spacer acquisition during CRISPR-Cas adaptive immunity
James K Nuñez1, Amy S Y Lee2, Alan Engelman3
1Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA.
Nature
|February 25, 2015
Summary
The Cas1-Cas2 complex is the minimal machinery for CRISPR adaptive immunity, integrating foreign DNA spacers into bacterial genomes. This process generates immunological memory by mimicking retroviral integrases and transposases.
Area of Science:
- Microbiology
- Molecular Biology
- Immunology
Background:
- Bacteria and archaea use CRISPR loci to store foreign DNA sequences as immunological memory.
- The molecular mechanism of spacer acquisition by the Cas1-Cas2 complex in E. coli remains largely unknown.
Purpose of the Study:
- To elucidate the molecular mechanism of spacer DNA acquisition mediated by the Escherichia coli Cas1-Cas2 complex.
- To identify the minimal machinery required for CRISPR-mediated adaptive immunity.
Main Methods:
- Purification of the Cas1-Cas2 complex.
- In vitro integration assays using oligonucleotide DNA substrates and supercoiled target DNA.
Main Results:
- The Cas1-Cas2 complex integrates protospacer DNA into acceptor DNA, similar to retroviral integrases and transposases.
- Cas1 is the catalytic subunit, with Cas2 significantly enhancing integration activity.
- Integration preferentially occurs at CRISPR repeat ends and AT-rich regions adjacent to cruciform structures.
Conclusions:
- The Cas1-Cas2 complex represents the minimal machinery for catalyzing spacer DNA acquisition.
- CRISPR repeats provide essential sequence and structural specificity for Cas1-Cas2-mediated adaptive immunity.
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