Nucleic acid modification and identification method

A method of identifying a polynucleic acid (PNA) comprising the steps of:

• providing a PNA;
• modifying one or more nucleobases of the PNA by addition or removal of a hydrogen bonding partner, thereby altering the base pairing capacity of the one or more nucleobases;
• base pairing a complementary nucleic acid to the PNA, including base pairing to at least one modified nucleobase;
• identifying the sequence of the complementary nucleic acid at least at the position that is complementary to at least one modified nucleobase;
• wherein base pairing to at least one modified nucleobase leads to base paring with another nucleotide than base pairing with a nucleobase that has not been modified, with said nucleobases being otherwise the same;
• wherein one or more cells are cultured or grown in at least two culturing or growth phases, wherein one culturing or growth phase comprises incorporation of a modified nucleotide into biosynthesized PNA, which is modified by addition or removal of a hydrogen bonding partner, and another culturing or growth phase that lacks such incorporation of the modified nucleotide into biosynthesized PNA or wherein modified nucleotides are incorporated into biosynthesized PNA at a different concentration as in the other one culturing or growth phase;
• or wherein the method comprises incorporation of a modified nucleotide into biosynthesized PNA of at least two different cells or into at least two different groups of cells.