DNA spontaneous mutation and its role in the evolution of GC-content: assessing the impact of the genetic sequence

The structure of DNA is not constantly at its equilibrium point but evolves with time. It is generally accepted that evolution induces a decrease of the guanine–cytosine (GC) content and a concomitant increase of the adenine–thymine (AT) ratio through a biased GC → AT mutation process. Unfortunately, the mechanism behind this natural alteration of the stored genetic information is not fully understood. Here, we use a hybrid QM:QM′ approach to assess the link between one of the sources of the spontaneous mutation, the so-called G*C* rare tautomers that arise from a double proton exchange between the bases, and the evolution of the GC-content. Our simulations indicate that the G*C* mutation is mainly accumulated in GC-rich regions rather than being randomly spread, and consequently the GC → AT error tends to locate in coding fragments. That specific preference is indirectly induced by the base pairs containing the mutated point, as they tune the structure of the first hydration-shell that solvates the reactive base pair undergoing tautomerisation. The reorganisation of the explicit water molecules eventually modifies the energy barriers as well as the stability of the genetic error during the process.