Research Article

Structure basis for RNA-guided DNA degradation by Cascade and Cas3

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Science  06 Jul 2018:
Vol. 361, Issue 6397, eaat0839
DOI: 10.1126/science.aat0839

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Target degradation of Type I CRISPR

The CRISPR adaptive immune systems defend bacteria against invaders. Type I CRISPR-Cas systems, the most prevalent type, use a Cascade complex to search the target DNA that is then degraded by Cas3 protein. Xiao et al. report cryo–electron microscopy structures of the Type I-E Cascade/Cas3 complex in the pre– and post–DNA-nicking states. These structures reveal how Cas3 captures Cascade only in its correct conformation to reduce off-targeting and how Cas3 switches from the initial DNA-nicking mode to the processive DNA degradation mode.

Science, this issue p. eaat0839