Restriction enzyme

Restriction enzyme glossary
Restriction The cutting of DNA at specific sites
Enzyme A protein that catalyzes a chemical reaction
Molecular recognition Used by restriction enzymes to locate specific sequences of DNA on which to bind and subsequently cleave
Recognition sequence The DNA sequence to which restriction enzymes bind
Restriction site The site of the DNA sequence where it is cleaved by the restriction enzyme
Restriction fragment A DNA fragment resulting from the cutting of a DNA strand by a restriction enzyme
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A restriction enzyme, restriction endonuclease, REase, ENase or restrictase is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites.^[1][2][3] Restriction enzymes are one class of the broader endonuclease group of enzymes. Restriction enzymes are commonly classified into five types, which differ in their structure and whether they cut their DNA substrate at their recognition site, or if the recognition and cleavage sites are separate from one another. To cut DNA, all restriction enzymes make two incisions, once through each sugar-phosphate backbone (i.e. each strand) of the DNA double helix.

These enzymes are found in bacteria and archaea and provide a defense mechanism against invading viruses.^[4][5] Inside a prokaryote, the restriction enzymes selectively cut up foreign DNA in a process called restriction digestion; meanwhile, host DNA is protected by a modification enzyme (a methyltransferase) that modifies the prokaryotic DNA and blocks cleavage. Together, these two processes form the restriction modification system.^[6]

More than 3,600 restriction endonucleases are known which represent over 250 different specificities.^[7] Over 3,000 of these have been studied in detail, and more than 800 of these are available commercially.^[8] These enzymes are routinely used for DNA modification in laboratories, and they are a vital tool in molecular cloning.^[9][10][11]