Thermodynamic properties of damaged DNA and its recognition by xeroderma pigmentosum group A protein and replication protein A.

The effects of the lesions induced by single, site-specific 1,2-GG or 1,3-GTG intrastrand adducts of cis-diamminedichloroplatinum(II) formed in oligodeoxyribonucleotide duplexes on energetics of DNA were examined by means of differential scanning calorimetry. These effects were correlated with affinity of these duplexes for damaged-DNA binding-proteins XPA and RPA; this affinity was examined by gel electrophoresis. The results confirm that rigid DNA bending is the specific determinant responsible for high-affinity interactions of XPA with damaged DNA, but that an additional important factor, which affects affinity of XPA to damaged DNA, is a change of thermodynamic stability of DNA induced by the damage. In addition, the results also confirm that RPA preferentially binds to DNA distorted so that hydrogen bonds between complementary bases are interrupted. RPA also binds to non-denaturational distortions in double-helical DNA, but affinity of RPA to these distortions is insensitive to alterations of thermodynamic stability of damaged DNA.