nick translation

A technique used to radioactively label DNA. E.coli DNA polymerase I will add a nucleotide, copying the complementary strand, to the free 3\'-OH group at a nick, at the same time its exonuclease activity removes the 5\'-terminus. The enzyme then adds a nucleotide at the new 3\'-OH and removes the new 5\'-terminus. In this way one strand of the DNA is replaced starting at a nick, which effectively moves along the strand. Nick translation refers to this translation or movement and not to protein synthesis. In practice, DNA is mixed with trace amounts of DNAase I to generate nicks, DNA polymerase I and labelled nucleotides. Because the nicks are generated randomly the DNA preparation can be uniformly labelled and to a high degree of specific activity.