Theoretical description of the coding potential of diamino-5-formamidopyrimidines

The results of geometry optimisation of possible Watson-Crick-like pairs of 2,6-diamino-4-oxy-5-formamidopyrimidine (fapy-adenine) or 4,6-diamino-5-fo rmamidopyrimidine (fapy-guanine) were presented. In the absence of the exte rnal field the fapy-adenine is able to form pairs with all four canonical n ucleic acid bases. However, pairs with guanine, cytosine and thymine the mo st stable are. Thus, the potential miscoding abilities may be observed. In contrast, in the presence of the external field the mispairing abilities of fapy-adenine become insignificant since the most stable dimers are formed with thymine. The pairing properties of fapy-guanine are complex and depend on its tatome ric form. In the absence of an external field the 4-enol-6-keto-diamino tau tomer of fapyG is able to form stable dimers with thymine and cytosine, whi le the 4,6-diketo-diamino tautomer forms the most stable pairs with cytosin e and guanine. The presence of the water solvent does not significantly alt er the pairing abilities of fapy-guanine. However, pairs with thymine are a t least as stable as the Watson-Crick GC pair. Thus, in polar conditions th e mispairing potential of fapyG will be extended and may be enriched by pot ential GC --> AT transition.