Inversion of the relative stability of AT- and GC-pairs in DNA induced by adsorption of ligands

The inversion of relative stability of AT- and GC-pairs of bases in the complexes of a block sequence DNA with long-range interacting ligands and DNA with random sequence of pairs of bases with contactly interacting ligands has been theoretically studied. Both types of ligand interaction with DNA are shown to give rise to a nonlinearity of the GC-content dependence of the melting temperature (Tm(x)), which induces a considerable increase in the melting range width (ΔT) at the inversion point. It is found that only short noninteracting ligands which are bound stronger to the boundaries between the helix and coil regions cause both the growth of ΔT at the inversion point and a linearity of the Tm (x) dependence.