Restriction endonucleases have become essential in biotechnology. This enzymes, produced in bacteria, archaea and Chlorella viruses, hydrolyze foreign DNA as a defence mechanism. There are four types of restriction endonucleases which differ in their recognition sequence, subunit composition, cleavage position, and cofactor requirements. Type II restriction endonucleases digest specific palindromic sequences of double-stranded DNA. Structural domains comprising this superfamily share the structure of the type II restriction endonuclease HindIII, produced in Haemophilus influenzae, which digests DNA at the palindromic sequence A/AGCTT PMID:19966419.