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.
Restriction endonucleases (ENases) are products of bacteria, and can be used to map a piece of DNA.
Some endonucleases have actions on RNA, such as the Dicer enzyme, which initiates the formation of RNA-induced silencing complexes. These may also be termed endoribonucleases.
1. UvrABC endonuclease is a well-documented endonuclease found in E.coli.
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