Nick translation is a technique 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. It can also be used for radioactive labeling in techniques such as Southern blotting.

This process is called nick translation because the DNA to be labelled is treated with DNase to produce single-stranded "nicks." This is followed by replacement in nicked sites by DNA polymerase I, which elongates the 3' end, removing nucleotides by 5'-3' exonuclease activity, and replacing them with dNTPs. To label a DNA fragment for use as a probe in blotting one of the incorporated nucleotides provided in the reaction is radiolabeled, or a fluorophore can be attached instead for fluorescent labelling, or is used as an antigen for immunodetection.

Sephadex G-50 DNA Grade can be used in a wide range of applications, including desalting DNA, buffer exchange, and removal of unincorporated nucleotides from end-labelled oligonucleotides. Sephadex G-50 can be packed into empty MicroSpin columns for use in these applications.

Sephadex G-50 is one of five different G-types ranging from G-10 for small molecules to G-75 for larger molecules. Sephadex G-50 is a well-established gel filtration resin for desalting and buffer exchange of biomolecules > 30 000 molecular weight, and with a spin protocol can be used for DNA and oligo purification of molecules greater than 20 bases in length. Alternatively, Sephadex G-25 can be used. Sephadex G-25 has an exclusion limit of approximately Mr 5000, and with a spin protocol this means it can be used for any DNA greater than 10 bases in length.

Both types of Sephadex are therefore highly suitable for the purification of oligonucleotides or very small DNA fragments following synthesis or in radioactive labeling.

Sephadex G-25 DNA Grade and Sephadex G-50 DNA Grade are sold separately.