Using nucleotides that contain a fluorescent moiety attached to the terminal phosphate offers a distinct advantage over directly labeling the nucleotide base.6–9 As the terminal phosphate-labeled nucleotide is incorporated into the growing DNA strand, the phosphodiester bond formation between the 3′-hydroxyl terminus of the DNA strand and the γ-phosphate of the incoming deoxyribonucleoside triphosphate releases the labeled pyrophosphate, resulting in the formation of an unmodified DNA strand.