Restriction Enzymes

One of the basic tools used in biotechnology is restriction enzymes. In natural circumstances, one of the main roles of these enzymes is to break foreign DNA entering the cell. A restriction enzyme breaks the phosphodiester bonds of a DNA upon appearance of a certain cleavage sequence. Each such enzyme is characterized by a different cleavage sequence. Today there are more then 150 known different cleavage sites, namely, different nucleotide configurations that known enzymes can digest.