Why only restriction endonuclease II only used in recombinant DNA technology and not I and III?
Sarthak Basak last edited by
There are three classes of restriction enzymes, labeled types I, II, and III.
Type I restriction systems consist of a single enzyme that performs both modification (methylation) and restriction activities. These enzymes recognize specific DNA sequences, but cleave the DNA strand randomly, at least 1,000 base pairs (bp) away from the recognition site.
Type III restriction systems have separate enzymes for restriction and methylation, but these enzymes share a common subunit. These enzymes recognize specific DNA sequences, but cleave DNA at random sequences approximately twenty-five bp from the recognition sequence.
Neither type I nor type III restriction systems have found much application in recombinant DNA techniques.
Type II restriction enzymes, in contrast, are heavily used in recombinant DNA techniques. Type II enzymes consist of single, separate proteins for restriction and modification. One enzyme recognizes and cuts DNA, the other enzyme recognizes and methylates the DNA.
Type II restriction enzymes cleave the DNA sequence at the same site at which they recognize it.