InterPro domain: IPR011335

Type II restriction endonucleases ( 3.1.21.4 ) are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. These site-specific deoxyribonucleases catalyse the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. Of the 3000 restriction endonucleases that have been characterised, most are homodimeric or tetrameric enzymes that cleave target DNA at sequence-specific sites close to the recognition site. For homodimeric enzymes, the recognition site is usually a palindromic sequence 4-8 bp in length. Most enzymes require magnesium ions as a cofactor for catalysis. Although they can vary in their mode of recognition, many restriction endonucleases share a similar structural core comprising four beta-strands and one alpha-helix, as well as a similar mechanism of cleavage, suggesting a common ancestral origin [ 1 ]. However, there is still considerable diversity amongst restriction endonucleases [ 2 , 3 ]. The target site recognition process triggers large conformational changes of the enzyme and the target DNA, leading to the activation of the catalytic centres. Like other DNA binding proteins, restriction enzymes are capable of non-specific DNA binding as well, which is the prerequisite for efficient target site location by facilitated diffusion. Non-specific binding usually does not involve interactions with the bases but only with the DNA backbone [ 4 ].

This superfamily represents the core structure found in most type II restriction endonucleases, consisting of a 3-layer alpha/beta/alpha topology with mixed beta-sheets. This core structure can be found in the restriction endonucleases EcoRI, EcoRV, BamHI, BglI, BglII, BstyI, PvuII, MunI, NseI, NgoIV, BsobI, HincII, MspI, FokI (C-terminal), EcoO109IR, as well as in lamba exonuclease, DNA mismatch repair protein MutH, VSR (very short repair) endonucleases, TnsA endonucleases (N-terminal), endonucleases I (Holliday junction resolvase), Hjc-like enzymes, XPF/Rad1/Mus81 nucleases, RecB and RecC exodeoxyribonuclease V (C-terminal), and RecU-like enzymes.

1. Type II restriction endonucleases: structure and mechanism. Cell. Mol. Life Sci. 62, 685-707
2. Diversity of type II restriction endonucleases that require two DNA recognition sites. Nucleic Acids Res. 31, 6079-84
3. Evolutionary relationship between different subgroups of restriction endonucleases. J. Biol. Chem. 277, 14306-14
4. Structure and function of type II restriction endonucleases. Nucleic Acids Res. 29, 3705-27