((11 ) )End labellingEnd labelling•The enzyme polynucleotide kinase is used The enzyme polynucleotide kinase is used to transfer the terminal phosphate group to transfer the terminal phosphate group of a radiolabelled ATP into 5- hydroxyl of a radiolabelled ATP into 5- hydroxyl termini of nucleic acid, which was termini of nucleic acid, which was dephosphorylated using phosphatase.dephosphorylated using phosphatase.

* This produces alabelled nucleic acid of * This produces alabelled nucleic acid of relatively low specific activity, as only the relatively low specific activity, as only the termini become radioactive termini become radioactive )Fig 10()Fig 10(

Nick translationNick translation•The enzyme The enzyme DNA polymerase IDNA polymerase I is used to is used to translate a nick created in the phosphodiester translate a nick created in the phosphodiester backbone of the DNA double helix.backbone of the DNA double helix.

•Nicks may occur naturally, or may be caused by Nicks may occur naturally, or may be caused by a low concentration of the a low concentration of the nuclease DNase.nuclease DNase.

* * DNA polymerase IDNA polymerase I catalyses a strand catalyses a strand replacement reaction which incorporates new replacement reaction which incorporates new dNTP into the DNA chain dNTP into the DNA chain )Fig 11(.)Fig 11(.