INFLUENCE OF MINOR-GROOVE BINDERS ON THE EUKARYOTIC TOPOISOMERASE-II CLEAVAGE REACTION WITH 41 BASE-PAIR MODEL OLIGONUCLEOTIDES

This report deals with the cleavage reaction of calf thymus (CT) topoi somerase II with oligonucleotides containing one main cleavage site an d adjacent binding sites for minor groove binders. The sequences of th e oligonucleotides were derived from a PER 322 sequence, which contain s one main topoisomerase II cleavage site. The cleavage reaction was p erformed under increasing concentrations of minor groove binders and i t showed characteristic inhibition dependences of topoisomerase II to the binding sites and to the binding length of the minor groove binder s. The extension of the minor groove binder length on DNA from 4 to 10 base pairs (bp) by netropsin and bis-netropsin, respectively, causes a strong increase of the topoisomerase II cleavage inhibition. The sam e is observed by the introduction of a second minor groove binder sequ ence symmetrically positioned around the topoisomerase II main cleavag e site. The combination of two different minor groove binders can lead to an increased topoisomerase II inhibition but also to a prevention of total inhibition as shown with chromomycin A, and distamycin A(3) a t concentrations of 0.1 and 0.25 mu M, respectively.