restriction endonuclease

A restriction enzyme (or restriction endonuclease) is an enzyme that cuts double-stranded DNA. The enzyme makes two incisions, one through each of the sugar-phosphate backbones (i.e., each strand) of the double helix without damaging the nitrogenous bases. The chemical bonds that the enzymes cleave can be reformed by other enzymes known as ligases, so that restriction fragments carved from different chromosomes or genes can be spliced together, provided their ends are complementary (more below). Many of the procedures of molecular biology and genetic engineering rely on restriction enzymes. The term restriction comes from the fact that these enzymes were discovered in E. coli strains that appeared to be restricting the infection by certain bacteriophages. Restriction enzymes therefore are believed to be a mechanism evolved by bacteria to resist viral attack and to help in the removal of viral sequences. They are part of what is called the restriction modification system.
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Restriction endonuclease one of over 200 enzymes isolated from bacteria that cleave any DNA molecule at specific sites which are usually palindromes [more]Restriction endonuclease - Community and Resources

Noun
1. 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
(synonym) restriction nuclease, restriction enzyme
(hypernym) endonuclease

An enzyme from bacteria that can recognize specific base sequences in DNA and cut (restrict) the DNA at that site (the restriction site). Also called a restriction enzyme.

an enzyme able to cleave the phosphodiester bonds within a nucleic acid strand by binding to DNA at a specific site.