The CRISPR editing tool has its origins in microbes - bacteria and archaea that live in obscene numbers everywhere from undersea vents to the snot in the human nose. All stripes of CRISPR. Scientists have divided the array of known CRISPR systems into five types and 16 subtypes based on DNA sequence data.
That’s because those phages have small proteins that will bind to and interfere with this or that part of the CRISPR machinery, such as the Cas enzyme that cuts phage DNA. The binding disables the CRISPR system, the researchers reported in 2015 in Nature.
In an especially bizarre twist, microbiologist Kimberley Seed of the University of California, Berkeley found a phage that carries its own CRISPR system and uses it to fight back against the cholera bacterium it invades, she and colleagues reported in 2013 in Nature.
You do need to let some DNA in, and it’s likely that some CRISPR systems permit this: The system he studies in Staphylococcus epidermidis, for example, only goes after phages that are in their cell-killing, or lytic, state, he and colleagues reported in 2014 in Nature.
So even as they scratch their heads about many things CRISPR, scientists are also excited by the stories CRISPR clusters can tell about the viruses and other bits of DNA that bacteria and archaea encounter and that they choose, for whatever reason, to note for the record.
This article appears in the April 15, 2017, issue of Science News with the headline, “The Original CRISPR: Before becoming a famous tool, the gene editor was a weapon in an unending microscopic war.”