The cutting of DNA at specific locations became possible with the discovery of restriction enzymes which are also called as molecular scissors or knife.
Restriction enzymes recognize dsDNA nucleotides as target sequences called restriction sites and cut the DNA at or near those sequences. Restriction enzymes bind to double-stranded DNA and cleave it at specific sites. Different restriction sites recognize different sequences. Type II restriction enzymes recognize palindromic sequences: four, five, or six base pairs in length. To date, more than 900 other restriction enzymes have been discovered from 230 strains of bacteria.