ddATP
ddATP, short for dideoxyadenosine triphosphate, is a dideoxynucleotide used as a chain-terminating substrate in DNA sequencing, notably the Sanger method. It differs from the regular dATP by lacking the 3' hydroxyl group on the deoxyribose sugar, which prevents the formation of the next phosphodiester bond and thus halts DNA synthesis after its incorporation. When a DNA polymerase incorporates ddATP opposite a template thymine, the growing DNA strand cannot be extended further.
In traditional Sanger sequencing, small amounts of ddATP are included with the standard deoxynucleoside triphosphates (dNTPs).
ddATP is one of the four chain-terminating nucleotides and is used in contexts where a thymine in
See also: Sanger sequencing, ddNTP, dNTP, chain termination.