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Updated: Jan 26, 2026

Substrate Generation for Endonucleases of CRISPR/Cas Systems
Published on: September 8, 2012
Predicted highly derived class 1 CRISPR-Cas system in Haloarchaea containing diverged Cas5 and Cas7 homologs but no
Kira S Makarova1, Svetlana Karamycheva1, Shiraz A Shah2
1National Center for Biotechnology Information, National Library of Medicine, 8600 Rockville Pike, Bethesda, MD 20894, USA.
Abstract:
Screening of genomic and metagenomic databases for new variants of CRISPR-Cas systems increasingly results in the discovery of derived variants that do not seem to possess the interference capacity and are implicated in functions distinct from adaptive immunity. We describe an extremely derived putative class 1 CRISPR-Cas system that is present in many Halobacteria and consists of distant homologs of the Cas5 and Cas7 protein along with an uncharacterized conserved protein and various nucleases. We hypothesize that, although this system lacks typical CRISPR effectors or a CRISPR array, it functions as a RNA-dependent defense mechanism that, unlike other derived CRISPR-Cas, utilizes alternative nucleases to cleave invader genomes.
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