The high-precision biological tool for making recombinant DNA is a special class of enzymes that cuts across a double helix in an interesting way. These special cutting enzymes, called restriction endonucleases, or restriction enzymes are widespread among bacteria. Their properties were first investigated in the 1960s by Werner Arber, a Swiss biochemist at the University of Geneva and a 1978 Nobel laureate.

Acting like scissors that can cut the DNA of viruses, they protect their owners from viral infection and restrict the range of viruses that can successfully invade. Hundreds of different restriction enzymes have been isolated from many species of bacteria; each recognizes a unique target sequence of usually four to seven bases.

 

 

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