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Mol Cell. 2015 Apr 2;58(1):60-70. doi: 10.1016/j.molcel.2015.01.028. Epub 2015 Mar 5.

Two distinct DNA binding modes guide dual roles of a CRISPR-Cas protein complex.

Author information

Kavli Institute of NanoScience and Department of BioNanoScience, Delft University of Technology, 2628 CJ, Delft, The Netherlands.
Laboratory of Microbiology, Department of Agrotechnology and Food Sciences, Wageningen University, 6703 HB, Wageningen, The Netherlands.
Contributed equally


Small RNA-guided protein complexes play an essential role in CRISPR-mediated immunity in prokaryotes. While these complexes initiate interference by flagging cognate invader DNA for destruction, recent evidence has implicated their involvement in new CRISPR memory formation, called priming, against mutated invader sequences. The mechanism by which the target recognition complex mediates these disparate responses-interference and priming-remains poorly understood. Using single-molecule FRET, we visualize how bona fide and mutated targets are differentially probed by E. coli Cascade. We observe that the recognition of bona fide targets is an ordered process that is tightly controlled for high fidelity. Mutated targets are recognized with low fidelity, which is featured by short-lived and PAM- and seed-independent binding by any segment of the crRNA. These dual roles of Cascade in immunity with distinct fidelities underpin CRISPR-Cas robustness, allowing for efficient degradation of bona fide targets and priming of mutated DNA targets.

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