DNA BREAKAGE AND INACTIVATION RESULTING FROM HYDROXYLAMINE AND OR CIS-DIAMMINEDICHLOROPLATINUM(II) INTERACTIONS WITH PLASMID DNA

1. Occurrence of lesions induced in plasmid DNA by cis-DDP and by HA w as quantified both as a transforming activity and as conformation inte grity of supercoiled pBR322 DNA. Fifty per cent decrease of the biolog ical activity of plasmid DNA, not accompanied by measurable change or DNA conformation, was observed after a single exposure of DNA to cis-D DP (I hr/37-degrees-C). 2. HA induced conversion of supercoiled DNA to other topological forms in a dose-dependent manner. 3. One- and two-s trand DNA breaks were determined electrophoretically with high sensiti vity. Cis-DDP exposed DNA relaxed at 30 times lower HA concentration c ompared to intact DNA. 4. This effect may be connected with a local di stortion of DNA structure at the cis-DDP-DNA bond, which makes possibl e high effectivity of HA-DNA interaction. 5. On other hand, biological activity stayed at the 50% level despite breaks induced in DNA. 6. Th is finding supports the idea that DNA breaks occur at the locations wh ich were modified during the exposure of DNA to cis-DDP. 7. The import ance of the DNA structure during interaction with HA may be seen durin g HA-DNA interaction at heat-denaturation of supercoiled DNA. At this condition, the DNA breaks were induced at 100 times lower concentratio n of HA. 8. We conclude, on the basis of these results and results pub lished earlier, that local distortion of supercoiled DNA structure, wh ich is caused by the cis-DDP bond, and the local DNA uncoiling caused by heat-denaturation are related to high HA-DNA reactivity.