Brad Plumer, Eliza Barclay, Julia Belluz, and Umair Irfan in Vox:
If we want to understand CRISPR, we should go back to 1987, when Japanese scientists studying E. coli bacteria first came across some unusual repeating sequences in the organism’s DNA. “The biological significance of these sequences,” they wrote, “is unknown.” Over time, other researchers found similar clusters in the DNA of other bacteria (and archaea). They gave these sequences a name: Clustered Regularly Interspaced Short Palindromic Repeats — or CRISPR.
Yet the function of these CRISPR sequences was mostly a mystery until 2007, when food scientists studying the Streptococcus bacteria used to make yogurt showed that these odd clusters actually served a vital function: They’re part of the bacteria’s immune system.
See, bacteria are under constant assault from viruses, so they produce enzymes to fight off viral infections. Whenever a bacterium’s enzymes manage to kill off an invading virus, other little enzymes will come along, scoop up the remains of the virus’s genetic code and cut it into tiny bits. The enzymes then store those fragments in CRISPR spaces in the bacterium’s own genome.
More here.