noun, plural: restriction enzymes
These enzymes are normally produced in bacteria and archaea as a defense mechanism against foreign DNA, especially of bacteriophages. The enzymes can be classified into Types I, II and III according to their mechanism of action.
The enzymes are named after the bacteria from where they are derived, i.e. the bacterial genus, species, strain and the order of identification. For instance, Eco RI is a restriction enzyme isolated from the bacteria: Escherichia (genus) coli (species) R (RY13 strain) I (first identified).