ddTTP
ddTTP, or dideoxythymidine triphosphate, is a nucleotide analog used as a chain-terminating substrate in Sanger DNA sequencing. It is the triphosphate form of dideoxythymidine, a sugar lacking both the 2' and 3' hydroxyl groups. The absence of the 3'-OH group prevents the formation of the next phosphodiester bond, so once ddTTP is incorporated by DNA polymerase, DNA synthesis stops.
In the Sanger method, a DNA polymerase reaction contains normal deoxynucleotides (dNTPs) and small amounts of
ddTTP is one of the four ddNTPs used in Sanger sequencing, alongside ddATP, ddCTP, and ddGTP. The