ddGTP

ddGTP stands for dideoxyguanosine triphosphate, a 2',3'-dideoxynucleotide triphosphate used as a chain-terminating reagent in Sanger DNA sequencing. Like other ddNTPs, ddGTP lacks the 3' hydroxyl group, so once it is incorporated by DNA polymerase, no further nucleotides can be added to the growing DNA strand, producing a terminated fragment.

In the Sanger sequencing method, ddGTP is included in the reaction mixture at low, controlled concentrations alongside the regular deoxynucleoside triphosphates (dNTPs). When a base on the template calls for incorporation of a G, a ddGTP may be incorporated instead of a regular dGTP, terminating that DNA fragment. By using four separate ddNTPs (ddATP, ddCTP, ddGTP, and ddTTP), each with a distinct detectable label, a collection of terminated fragments of varying lengths is generated. After separation by gel or capillary electrophoresis, the terminating bases are read to infer the sequence.

ddGTP and the other ddNTPs played a pivotal role in the original Sanger method, enabling precise, dye- or radioactively labeled readouts of nucleotide sequences. Although newer sequencing technologies have largely supplanted traditional Sanger workflows with alternative chemistries and detection systems, ddGTP remains a key historical and educational reference for chain-termination sequencing concepts.