[Interrelation of the electronic structure of nucleic acid components and their ability and specificity in template...

A hypotesis suggesting that the specificity of polynucleotide template synthesis is based not on complementarity but on the correspondence of the electronic structure of the precursor and the enzyme active site (EAS), the latter being formed by the template, enzyme, and, possibly, by the polynucleotide synthesized is described. Comparison of the electronic structure of natural nucleic bases and their analogs allows to suppose that the EAS discriminates between adenine and cytosine, and uracil (thymine) and guanine, by electrostatic features: sign of the potential in the region of exocyclic substituents at C(4) of pyrimidines and C(5) of purines. For adenine and cytosine this sign is positive while for uracil (thymine) and guanine it is negative. The second feature allowing to discriminate between purines and pyrimidines is connected with general difference of their electronic structure. The total charge of N-glycoside center, more negative for pyrimidines, can serve as an index of this difference. According to the hypothesis the compounds unable to form complementary pairs can be functionally active in the polynucleotide template synthesis and can show ambiguous functional specificity due not only to the presence of different ionic and/or tautomeric species but also to the potential in the aforementioned region being close to zero or the charge of N-glycoside center being intermediate. It can be assumed that for the formation of EAS the same features of the electronic structure of the nucleotide residues of the template are used, which are important for the interaction of the precursor with the EAS (recognition of the precursor).