Types of Restriction Endonucleases - There are three distinct types of restriction endonucleases. Type I restriction endonucleases are complex endonucleases, and have recognition sequences of about 15 bp; they cleave the DNA about 1000 bp away from the 5'-end of the sequence "TCA" located within the recognition site, e.g., EcoK, EcoB etc.

Type II restriction endonucleases are remarkably stable and induce cleavage either, in most cases, within their recognition sequences or very close to them. More than 350 different type II endonucleases with over 100 different recognition sequences are known. They require Mg²⁺ ions for cleavage.