Restriction enzymes are naturally produced by bacteria. Since their discovery, they have played a fundamental role in genetic engineering. These enzymes recognize and cut at specific locations in the double helix of DNA and have made it possible for advancements in such areas as genetic therapy and pharmaceutical production.

A restriction enzyme is a more common name for a restriction endonuclease. Restriction enzymes are proteins found in bacterial cells that recognize specific short DNA (deoxyribonucleic acid as well as gene therapies.

There are thousands of different restriction enzymes, each one named for the bacteria from which it originated. These enzymes recognize and cut hundreds of unique DNA sequences, typically four to seven base units long. Scientists select which specific restriction enzyme to use based on the desired result.

Restriction enzymes work by targeting a specific sequence of base pairs in DNA. DNA has four nucleotide bases that pair together; adenine pairs with thymine, and cytosine pairs with guanine. The restriction enzyme causes both strands of the DNA to break apart, often resulting in DNA molecules with protruding unpaired bases, or sticky ends. These sticky ends can be bonded together with complementary DNA base pairs cut with the same restriction enzyme, even if the DNA is from an entirely different species.

In order for a gene to work, it cannot simply be inserted directly into a cell. First, scientists must use restriction enzymes to splice, or cut out, the gene they want to use. The same restriction enzyme then is used to open the DNA in a host cell, or vector, which delivers the DNA. The vector can be bacterial or viral. If the goal is to produce large quantities of the desired gene, bacterial cells typically are used. If the goal is for gene therapy, a modified viral cell is used that can infect specific parts of a cell in order to integrate the new genetic material.

The discovery of restriction enzymes has opened the doors for scientific advancements in gene therapy as well as pharmaceuticals. In 1982, human insulin produced in genetically engineered bacteria was the first recombinant product approved by the U.S. Food and Drug Administration for commercial use. Some scientists hope gene therapy ultimately can lead to treatments for diseases such as cancer, heart disease, AIDS and cystic fibrosis.