Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 536955
Title Repetitive DNA Reeling by the Cascade-Cas3 Complex in Nucleotide Unwinding Steps
Author(s) Loeff, Luuk; Brouns, Stan J.J.; Joo, Chirlmin
Source Molecular Cell 70 (2018)3. - ISSN 1097-2765 - p. 385 - 394.
DOI http://dx.doi.org/10.1016/j.molcel.2018.03.031
Department(s) Microbiological Laboratory
Publication type Refereed Article in a scientific journal
Publication year 2018
Keyword(s) adaptive - Cas3 - cascade - CRISPR - FRET - helicase - immunity - interference - single-molecule
Abstract

CRISPR-Cas provides RNA-guided adaptive immunity against invading genetic elements. Interference in type I systems relies on the RNA-guided Cascade complex for target DNA recognition and the Cas3 helicase/nuclease protein for target degradation. Even though the biochemistry of CRISPR interference has been largely covered, the biophysics of DNA unwinding and coupling of the helicase and nuclease domains of Cas3 remains elusive. Here, we employed single-molecule Förster resonance energy transfer (FRET) to probe the helicase activity with high spatiotemporal resolution. We show that Cas3 remains tightly associated with the target-bound Cascade complex while reeling the DNA using a spring-loaded mechanism. This spring-loaded reeling occurs in distinct bursts of 3 bp, which underlie three successive 1-nt unwinding events. Reeling is highly repetitive, allowing Cas3 to repeatedly present its inefficient nuclease domain with single-strand DNA (ssDNA) substrate. Our study reveals that the discontinuous helicase properties of Cas3 and its tight interaction with Cascade ensure controlled degradation of target DNA only. Loeff et al. report on a single-molecule fluorescence analysis of the E. coli CRISPR-Cas3 protein. The Cas3 protein uses a spring-loaded unwinding mechanism, reeling the target DNA 3 bp at a time. Facilitated by slipping, Cas3 repeatedly presents its intrinsically inefficient nuclease domain with DNA substrate, which may contribute to promoting a robust immune response.

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