METAL-ION ASSISTED, RADIATION-INDUCED CONVERSION OF B-DNA TO Z-DNA INPOLY (DGDC) AND 2 NATURAL DNAS

Metal-ion assisted, gamma-radiation-induced B-Z conformation changes h ave been observed with UV and circular dichroism spectroscopy for poly (dGdC), calf thymus and herring testis DNA. These conformational chan ges are similar to those induced by increasing multivalent metal ion c oncentrations in DNA containing alternating purine and pyrimidine base sequences. In both the metal-ion-induced and the metal-ion-assisted, radiation-induced conformation changes, the conversions were from the right-handed B-DNA to the left-handed Z-DNA conformation. It is propos ed that radiation-induced DNA strand breaks markedly reduce the high a ctivation energy barrier in the metal ion-driven B-Z conformation conv ersion and allow much smaller metal ion concentrations to induce this conversion than in the absence of strand breaks. The biological import ance of such radiation-induced conformational changes is discussed in terms of the potential significance of the Z-DNA conformation in the c ontrol of the DNA transcription process.