Using diffraction data obtained at Berkeley Lab’s Advanced Light Source (ALS) and at the Stanford Synchrotron Radiation Lightsource (SSRL), researchers in Biosciences’ Molecular Biophysics & Integrated Bioimaging (MBIB) division and at UC Berkeley have discovered how CRISPR-associated (Cas) proteins are able to recognize their target locations with such great specificity. X-ray crystallography was used to solve the structures of Cas1 and Cas2—responsible for DNA-snippet capture and integration—as they were bound to synthesized DNA strands designed to mimic different stages of the process. The resulting structures show how the system works in its native context as part of a bacterial immune system, and also inform the development of the CRISPR-Cas system as a general-purpose molecular recording device. Jun-Jie Liu, a joint postdoc in the labs of Jennifer Doudna and Eva Nogales, and Addison Wright, a graduate student in Doudna’s lab, were co-first authors on the paper, published in the journal Science. Read more in this ALS Science Highlight.