T OOLS OF R ECOMBINANT DNA T ECHNOLOGY Now we know from the foregoing discussion that genetic engineering or recombinant DNA technology can be accomplished only if we have the key tools, i.e., restriction enzymes, polymerase enzymes, ligases, vectors and the host organism. Let us try to understand some of these in detail. . .
Restriction Enzymes In the year , the two enzymes responsible for restricting the growth of bacteriophage in Escherichia coli were isolated. One of these added methyl groups to DNA, while the other cut DNA. The later was called restriction endonuclease . The first restriction endonuclease– Hind II , whose functioning depended on a specific DNA nucleotide sequence was isolated and characterised five years later.
It was found that Hind II always cut DNA molecules at a particular point by recognising a specific sequence of six base pairs. This specific base sequence is known as the recognition sequence for Hind II . Besides Hind II , today we know more than restriction enzymes that have been isolated from over strains of bacteria each of which recognise different recognition sequences. The convention for naming these enzymes is the first letter of the name comes from the genus and the second two letters come from the species of the prokaryotic cell from which they were isolated, e.g., EcoRI comes from E s cherichia coli RY .
In EcoRI, the letter ‘R’ is derived from the name of