Comparison of the binding of the therapeutically active nucleosides to DNA molecules with different level of lesions

Recently we have shown that DNA molecules extracted from epididymis of the Wistar male rats exposed to low doses of gamma radiation interact with some pyrimidine nucleosides. The bindign affinities of NUC to control DNA molecules are unessential. Comparing the UV melting curves for the various DNA sammples we show that observed differences are related to conformational chagnes in the DNA double helix. The samples of the damaged DNA have been obtained by partial denaturation of the calf thymus DNA in the salt-free aqueous solutions. The level of DNA damages in the model DNA smplase depends on the DNA concentration. It was shown that damages in the DNA molecules lead to changes of the melting curves of DNA-NUC mixtures that are similar to those for the DNA samples extracted from irradiated tissues. ALso it has been found that the binding mechanisms to cytosine arabinoside and 6-azacytosine to DNA molecuels having modifeid secondary structures are different.