The procedure for labeling of DNA probes with a polynucleotide "tail" containing hapten-labeled nucleotides was developed by Enzo. In such terminal labeling reactions, terminal transferase catalyzes the addition of nucleotides to any 3'-OH terminus in a template independent manner. This rapid and convenient nonradioactive labeling procedure is free of any sequence bias that is normally observed in random priming or nick translation reactions.

Terminal labeling is an ideal procedure for the labeling of oligonucleotides. An oligonucleotide can be synthesized using standard, commercially available reagents and labeled after synthesis in a simple and reproducible enzyme reaction. The BioProbe® 3'-Oligonucleotide Labeling System provides maximum flexibility for labeling oligonucleotides approximately 15 to 100 nucleotides in length. A standard reaction will label up to 100 picomoles (1µg of a 30-mer oligonucleotide sequence). A complete system combines a standard Reagent Pack (buffers and enzyme) with a Nucleotide Pack. All components contain sufficient reagents for 25 labeling reactions.The system is available in two modular formats:3'-Oligonucleotide Tailing (with a "tail" of nucleotides) 3'-Oligonucleotide Labeling (with a single nucleotide)The BioProbe® 3'-Oligonucleotide Labeling System Dideoxynucleotide Pack contains a vial of modified dideoxynucleotide and a vial of control oligonucleotide labeled with the modified dideoxynucleotide. Terminal labeling reactions using dideoxynucleotides result in the addition of a single nucleotide at the 3'-OH terminus. For optimum results, the nucleotide contained in this Pack should be used with the 3'-Oligonucleotide Labeling System Reagent Pack.