Patent ID: 8716457

Claim:
A method of characterising a nucleotide in a nucleic acid sequence, said method comprising: (a) contacting a nucleic acid with a peptide nucleic acid (PNA) oligomer capable of hybridising to a portion of the nucleic acid and lacking a base complementary to that of the nucleotide to be characterised, to form a nucleic acid/PNA duplex; and (b) contacting the nucleic acid/PNA duplex with modified bases selected from the group consisting of: Wherein Y is a functional group capable of reversible covalent reactions; X 1 -X 4 is a detectable tag, spacer-tag combination or hydrogen; and Z is carbon or nitrogen; wherein the modified base which integrates with the nucleic acid/PNA duplex is complementary to that of the nucleotide to be characterised, the nucleotide being characterised by mass spectrometry or by means of the detectable tag of the modified base.