Nick translation[1] (or head translation), developed in 1977 by Peter Rigby and Paul Berg, is a tagging technique in molecular biology in which DNA polymerase I is used to replace some of the nucleotides of a DNA sequence with their labeled analogues, creating a tagged DNA sequence which can be used as a probe in fluorescent in situ hybridization (FISH) or blotting techniques.
[3] To radioactively label a DNA fragment for use as a probe in blotting procedures, one of the incorporated nucleotides provided in the reaction is radiolabeled in the alpha phosphate position, often using phosphorus-32.
Similarly, a fluorophore can be attached instead for fluorescent labelling, or an antigen for immunodetection.
The nick has "translated" some distance depending on the processivity of the polymerase.
Proprietary enzyme mixes are available commercially to perform all steps in the procedure in a single incubation.