<Tr> <Th> PubMed </Th> <Td> articles </Td> </Tr> <Tr> <Th> NCBI </Th> <Td> proteins </Td> </Tr> <P> Typical type II restriction enzymes differ from type I restriction enzymes in several ways . They form homodimers, with recognition sites that are usually undivided and palindromic and 4--8 nucleotides in length . They recognize and cleave DNA at the same site, and they do not use ATP or AdoMet for their activity--they usually require only Mg as a cofactor . These enzymes cleave the phosphodiester bond of double helix DNA . It can either cleave at the center of both strands to yield a blunt end . Or it can cleave at a staggered position leaving overhangs called sticky ends . These are the most commonly available and used restriction enzymes . In the 1990s and early 2000s, new enzymes from this family were discovered that did not follow all the classical criteria of this enzyme class, and new subfamily nomenclature was developed to divide this large family into subcategories based on deviations from typical characteristics of type II enzymes . These subgroups are defined using a letter suffix . </P> <P> Type IIB restriction enzymes (e.g., BcgI and BplI) are multimers, containing more than one subunit . They cleave DNA on both sides of their recognition to cut out the recognition site . They require both AdoMet and Mg cofactors . Type IIE restriction endonucleases (e.g., NaeI) cleave DNA following interaction with two copies of their recognition sequence . One recognition site acts as the target for cleavage, while the other acts as an allosteric effector that speeds up or improves the efficiency of enzyme cleavage . Similar to type IIE enzymes, type IIF restriction endonucleases (e.g. NgoMIV) interact with two copies of their recognition sequence but cleave both sequences at the same time . Type IIG restriction endonucleases (e.g., Eco57I) do have a single subunit, like classical Type II restriction enzymes, but require the cofactor AdoMet to be active . Type IIM restriction endonucleases, such as DpnI, are able to recognize and cut methylated DNA . Type IIS restriction endonucleases (e.g., FokI) cleave DNA at a defined distance from their non-palindromic asymmetric recognition sites; this characteristic is widely used to perform in - vitro cloning techniques such as Golden Gate cloning . These enzymes may function as dimers . Similarly, Type IIT restriction enzymes (e.g., Bpu10I and BslI) are composed of two different subunits . Some recognize palindromic sequences while others have asymmetric recognition sites . </P>

Dna can be cut at specific sites by using restriction enzymes