DRUG STIMULATED DNA CLEAVAGE MEDIATED BY CAULIFLOWER TOPOISOMERASE-II

We have investigated cauliflower (Brassica oleracea) topoisomerase ll with respect to its interaction with DNA and demonstrate that the enzyme shares the characteristics of topoisomerase ll purified from a variety of phylogenetically remote organisms. In the presence of the 2-nitroimidazole Ro 15-0216, cauliflower topoisomerase ll-mediated DNA cleavage is extensively stimulated (approximately 20-fold) only at a site recognized as a major cleavage site for the enzyme in the absence of drug. The conservation of the enzyme's DNA specificity in the presence of Ro 15-0216 is in contrast to the effect exerted by traditional topoisomerase ll inhibitors, which cause enzyme-mediated cleavage to take place at a multiple number of DNA sites. Ro 15-0216 may therefore prove useful as a tool in the elucidation of the enzyme's DNA interaction sites and its involvement in nucleic acid metabolism in plant cells.