Method of sequencing DNA

A method of identifying a base at a target position in a sample nucleic acid sequence, said method comprising:

• subjecting a primer hybridized to said sample nucleic acid immediately adjacent to the target position, to a DNA polymerase primer extension reaction in the presence of a nucleotide and the nucleotide degrading enzyme apyrase, whereby the nucleotide will only become incorporated if it is complementary to the base in the target position, and determining whether or not said nucleotide is incorporated by detecting whether PPi is released, the identity of the target base being determined from the identity of any nucleotide incorporated,
• wherein, where said nucleotide comprises an adenine base, an α-thio triphosphate analogue of said nucleotide is used, and the Rp isomer of said analogue and/or the degradation products of said analogue are eliminated from the DNA polymerase reaction and nucleotide degradation step, and
• wherein said elimination reduces or avoids the inhibition of the nucleotide degrading enzyme apyrase which is present during or after the DNA polymerase reaction step.