Arber hypothesized that bacterial cells might express two types of enzymes: a restriction enzyme that recognizes and cuts up the foreign bacteriophage DNA and a modification enzyme that recognizes ...

“As soon as the Type II restriction enzymes were discovered—and HindII in particular—it was obvious that you could take a fairly large DNA and cut it into smaller pieces. And that offered you the ...

Various types of endonucleases – enzymes that can cut DNA – were already known before CRISPR-Cas9. The discovery of restriction enzymes in the early 1970s heralded a new age in molecular biology.