Long before they became the hottest trend in DNA-editing technology, CRISPR systems originated in bacteria as a defense against foreign DNA from invading viruses, also known as bacteriophages.
This animation shows a 3D molecular model (based on cryo-electron microscopy (cryo-EM) studies) of a CRISPR complex (Csy) binding to foreign DNA (orange). When the complex binds to the DNA, it stretches along its helical axis. This may be a key step in preparing the DNA for degradation by the associated Cas protein.
Based on research from Guo, T. W. et al. Cryo-EM Structures Reveal Mechanism and Inhibition of DNA Targeting by a CRISPR-Cas Surveillance Complex. Cell 171, 414–426.e12 (2017).
Molecular Models: PDB 6B44 and 6B45