PerspectiveStructural Biology

Cascading into focus

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Science  19 Sep 2014:
Vol. 345, Issue 6203, pp. 1452-1453
DOI: 10.1126/science.1260026

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Summary

An adaptive immune pathway in bacteria and archaea is specified by clustered, regularly interspaced, short palindromic repeat (CRISPR) sequences (1). Research into CRISPR RNAs (crRNAs) and the CRISPR-associated (Cas) proteins have revealed the ability of most of these systems to target foreign DNA molecules for destruction. On pages 1473 and 1479 of this issue, Jackson et al. (2) and Mulepati et al. (3), respectively, and Zhao et al. (4) describe high-resolution structures of the multiprotein assembly called CRISPR-associated complex for antiviral defense (“Cascade”), which drives CRISPR interference in many strains of Escherichia coli. The structures show how Cascade presents crRNA to its DNA target, and demonstrate that DNA recognition occurs through a configuration that, surprisingly, is not double-helical.