Question

Why are type II restriction endonucleases used for DNA cloning and not types I and III?

Answer 1

Restriction enzymes:

1. Restriction enzymes are the enzymes produced by certain bacteria that have the property of cleaving DNA molecules at or near specific base sequences.
2. Type I restriction enzyme cut the DNA randomly and far from the recognition site. Thus, it is not used for practical purposes.
3. Type II cut the DNA from the recognition site at the defined position. Their cut produces a sticky end of the DNA.
4. Type III restriction enzyme cut outside the recognition sequences requires two such sequences in opposite directions within the same DNA molecule to accomplish the cut. They rarely give complete digests.
5. Therefore, the Type II restriction enzyme is used for DNA cloning and not types I and III.