Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain, in contrast to exonucleases, which cleave phosphodiester bonds at the end of a polynucleotide chain. Restriction endonucleases (Restriction Enzymes) cleave DNA at specific sites, and are divided into three categories, Type I, Type II, and Type III, according to their mechanism of action. These enzymes are often used in genetic engineering to make recombinant DNA for introduction into bacterial, plant, or animal cells.

Common endonucleases:

Restriction endonucleases (ENases) are products of bacteria, and can be used to map a piece of DNA.


  1. UvrABC endonuclease is a well documented endonuclease found in E.coli.

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