[Effect of additional links weakening or stabilizing the double helix at the melting point of DNA].

Within the framework of the contemporary helix-coil transition theory the dependence of DNA melting temperature on the concentration of modified links stabilizing or destabilizing the double helix is calculated. The calculations show that at all values of the stabilization (destabilization) energy the shift in the melting temperature is strictly proportional to the concentration of modified links. The dependence of the slopes of these curves is calculated for the first time. The available data on the effect of chemical modification upon the DNA melting temperature are discussed in the light of the theoretically obtained results.