restriction enzyme

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of a group of enzymes that catalyze the cleavage of DNA at specific sites to produce discrete fragments, used especially in genetic engineering.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun genetics An endonuclease that catalyzes double-strand cleavage of DNA containing a specific sequence.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of the enzymes that cut nucleic acid at specific restriction sites and produce restriction fragments; obtained from bacteria (where they cripple viral invaders); used in recombinant DNA technology