restriction endonucleases play a very important role in modern molecular cloning techniques. because of their unique recognition/cut sites, restriction enzymes can be used to precisely cut dna at specific locations in a predictable manner. once cut, the dna (usually) possesses so-called "sticky ends", which can then allow the dna fragment to hybridise into a dna vector. ligating enzymes are used to covalently link the desired fragment to the vector for subsequent dna cloning.