Bacteria and archaea are under constant attack from foreign genetic elements. The CRISPR-Cas immune system affords protection from such invaders. Upon encountering foreign DNA, the CRISPR-Cas system creates DNA fragments that match the sequences of the invading foreign DNA and then inserts these DNA fragments, or “spacers” into the microbe's genome. That way, the next time the organism encounters something similar, it can quickly recognize it and defend against it through an RNA interference-like mechanism. By solving the crystal structures and performing additional biochemical analysis, Nuñez et al. now uncover the specific functions of the enzymes Cas1 and Cas2. Acting as a complex, Casl and Cas2 help bacteria and archaea acquire DNA spacers and insert them correctly into the host genome. - VV
Nat. Struct. Mol. Biol. 10.1038/nsmb.2820 (2014).