A nicking enzyme (or nicking endonuclease) is an enzyme that cuts one strand of a double-stranded DNA at a specific recognition nucleotide sequences known as a restriction site. Such enzymes hydrolyse (cut) only one strand of the DNA duplex, to produce DNA molecules that are “nicked”, rather than cleaved.^[1][2]

They can be used for strand-displacement amplification,^[3] Nicking Enzyme Amplification Reaction, exonucleotyic degradation, the creation of small gaps,^[4] or nick translation.^[5] The latter process has been successfully used to incorporate both radioactively labelled nucleotides and fluorescent nucleotides allowing specific regions on a double stranded DNA to be studied.^[5][6] Over 200 nicking enzymes have been studied, and 13 of these are available commercially^[7] and are routinely used for research and in commercial products.