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Introduction
What is a Restriction Endonuclease?
| Restriction endonucleases are enzymes that recognize specific sequences of DNA and cleave either within that site or right next to it. In bacteria, they function to prevent infection by viruses by choppping up the foriegn DNA, but are now used extensively in DNA recombination techniques, such as cloning, and for studying protein interactions with specific DNA sequences. They go their name because they restrict the host range of the virus and they cut in the middle of the DNA (endo), not at the ends. The recognition site is called a restriction site, and for most restriction endonucleases the site is six base pairs long. This website covers Type II restriction endonucleases. These non-specifically bind to DNA, then scan downstream until they find the restriction site. One or two metal ions (usually magnesium) are needed for cleavage to occur. Over 3000 of these enzymes are known, but crystal structures exist for only a handful of these.
Here is a picture of EcoRV grasping DNA. EcoRV is by far the best studied structure. |
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