Thermodynamics of a 24-mer triple helm formation and stability

In this work we report a thermodynamic characterization of stability and me lting behaviour of two 24-mer DNA triplexes. The third strand, that binds t he Watson-Crick double helix with Hoogsteen hydrogen bonds, contains 3'-3' phosphodiester junction that determines the polarity inversion. The target double helix is composed of adjacent and alternate fragments of oligopurine -oligopyrimidine tracts. The two helices differ from the substitution of th e cytosine, involved in the junction, with the thymine. Calorimetric data r eported here provide a quantitative measure of the influence of pH and base modification on the stability of a DNA tripler.