Restriction enzymes recognize foreign bacteriophages and cut their DNA, limiting their growth. Researchers use them to slice DNA into smaller pieces for study and to join molecules of DNA from distinct genomes for the purpose of studying gene regulation and expression or characterizing and identifying a gene.
The first study showing the function of restriction enzymes took place in 1971; the researchers used restriction enzymes to shred the DNA of SV40, a eukaryotic virus that has the ability to spur tumor growth. As of 2014, scientists use this same process, along with electrophoresis, to split fragments of DNA. Some researchers also use an RNA or DNA molecule that has a base sequence that matches a sequence of DNA in which they have interest to find the location of that particular sequence on a genome.
Using restriction enzymes to combine DNA from multiple organisms first took place in a 1972 study and relies on the way in which the restriction enzyme EcoR1 cuts its DNA in such a way as to leave ends that have one strand, called sticky or cohesive ends. When two of these ends join together, a different enzyme, DNA ligase, seals the bone together. This process has many applications with regard to joining fragments of DNA from multiple species; this is the area of restriction enzyme use that raises the most ethical questions.