Several computational studies have attempted to measure the minimum energy pathway (or transition state) of the tautomerisation reaction in both A-T and G-C base pairs. These studies have been detailed in reviews by Kim et al. and Srivastava 12 but vary in methodology and, consequently, have produced different conclusions about the stability of the A*-T* tautomeric base pair. Some studies suggest the configuration is metastable, some suggest that there is a shallow energy minimum and others suggest that there exists an energy minimum substantial enough to be considered a candidate for the spontaneous mutagenesis mechanism. 17