ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
Restriction enzymes, sometimes called restriction endonucleases, are short nucleotide sequences isolated from prokaryotic organisms that protect the cell from foreign DNA. Several hundred of these enzymes have been isolated from various organisms and most are available commercially. These enzymes recognize specific sequences, usually four to eight nucleotides in length. Different organisms produce enzymes with different sequence recognition sites, called restriction sites. Most organisms only recognize one specific site thus different enzymes will cut the same piece of DNA in different locations.
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