Alteration of the Relative Stability of dA{middle dot}dT and dG{middle dot}dC Base Pairs in DNA

摘要: Several small alkylammonium ions can eliminate, or even reverse, the usual dependence of DNA transition temperature on base composition. For example, in 3 M tetramethylammonium chloride, 2.4 tetraethylammonium DNAs different compositions all melt at a common temperature, and with greatly decreased breadth reflecting only sequence-independent components melting cooperativity. At still higher concentrations such additives, dG.dC-rich lower temperatures than dA.dT-rich molecules. Circular dichroism spectra show that these additives alter structure double helix very little room temperature. This differential (base-specific) effect stability is investigated several related to tetraalkylammonium ions. Additives larger ion have stability. Preferential binding dA.dT pairs, requiring fit into "groove" DNA, consistent data equilibrium studies. These effects be distinguished from general destabilizing effects, which are independent specific features macromolecular conformation chemistry. Possible experimental uses this ability base-composition-dependent discussed, as well insight phenomenon provides molecular basis for dG.dC pairs.