Enzymology. A bacterial enzyme that cuts DNA at specific sites. The function of restriction enzymes is to destroy any foreign DNA (e.g., virus) that invades the host cell. In genetic engineering they are used to cut and sequence DNA and build restriction fragments which can be inserted in other DNA molecules.
They are named according to the bacterium from which they are isolated. For example, EcoRI is the first enzyme isolated from the R strain of Escherichia coli.