Structural biologists show how the DNA-cutting enzyme at the heart of a powerful gene-editing system changes shape to slice through DNA.

Martin Jinek at the University of Zurich, Switzerland, and his colleagues studied the CRISPR–Cas system, in which an RNA molecule is used to guide and program the Cas enzyme to break through a specific segment of DNA.

The team used X-ray crystallography and single-particle electron microscopy to explore the structure of Cas9 enzymes from two different bacterial species. They found that when the Cas9 enzymes bind to the guide RNA, the active sites rearrange to form a central channel that can attach to DNA.

Furthermore, the Cas9 enzyme is easily programmed by certain guide RNAs because of the amino-acid sequence at the enzyme's active site, which allows the enzyme's shape to be customized.

Science http://doi.org/rcs (2014)