However, the double proton transfer product is biologically relevant to the spontaneous mutagenesis process as its tautomeric nucleobases can bond in non-canonical pairings that evade replisome fidelity checks. The conclusion that the A*-T* base pair can be a genetic mutation instigator is contrary to several previous studies which have only examined the tautomerisation of A-T while the DNA duplex is in an equilibrium state, finding that the state A*-T* at equilibrium is metastable and therefore biologically irrelevant.