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RESTRICTION ENDONUCLEASES

Recombinant DNA technology and gene cloning often needs enzymes that are capable of cutting double stranded DNA at specific sites or recognized regions which are also called recognition sequences. Such enzymes are termed as restriction endonucleases since they cut nucleic acids internally by restricting themselves to some specific recognition sequences.

On the outset the restriction endonucleases are a part of restriction enzymes which also includes restriction exonucleases. In fact the prefixes, endo- and exo- of the names of these enzymes implies to their mode of action. Exonucleases cut the outermost nucleotide or the nucleotide that is present at the end of the polynucleotide chain. Whereas, the endonucleases are capable of cutting anywhere it finds a specific restriction site along the polynucleotide sequence.

The presence of restriction endonucleases was first reported by W.Arber in 1960s. The Nobel Prize was awarded in 1978 for the discovery of endonucleases to Hamiltion Smith, Daniel Nathans and Werner Arber in Physiology and Medicine.

Ø      The strain from which it is taken is given by the letter following the species name which is always a normal (non-italic) alphabet.

Ø  The following roman numbers denote the first identification order.