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 illustration shows a 3D molecular model (based on cryo-electron microscopy (cryo-EM) studies) of a CRISPR complex (Csy) binding to foreign DNA (orange). It splits the two strands of DNA apart in order to prepare the DNA for degradation, thus protecting the bacterial cell from infection. This can mean the difference between death and survival for the bacteria (background).
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).
Veronica Falconieri/Subramaniam Lab/CCR/NCI/NIH