Restriction enzymes are DNA-cutting enzymes found in bacteria and harvested from them for use. Because they cut within the molecule, they are often called restriction endonucleases. A restriction enzyme recognizes and cuts DNA only at a particular sequence of nucleotides. So, restriction endonucleases are used for the separation of genetic material. Restriction endonuclease was discovered by Werner Arber, Hamilton O. Smith, and Daniel Nathans in the late 1960s and early 1970s.