Crystal-clear memories of a bacterium

Information storage in DNA is the cornerstone of biology. Interestingly, prokaryotes can store information in specific loci in their DNA to remember encounters with invaders (such as bacteriophages—viruses that infect bacteria). Short samples of DNA from invaders are inserted as “spacers” into the CRISPR array. The array thus contains samples of DNA invaders in a defined locus that is recognized by Cas proteins that further process this information. This enables bacteria to adaptively and specifically respond to invading DNA that they have experienced before. Structures of the molecular machinery catalyzing this memorization process have previously been solved ( 1 – 4 ), but not when bound to the CRISPR array. On page 1113 of this issue, Wright et al. ( 5 ) provide structures of this molecular machinery with artificial substrates that represent the CRISPR array in different stages of spacer insertion. Better understanding of how spacers are integrated into the CRISPR array in the memorization process will assist in harnessing it for future biotechnological applications.