ANALYSIS OF THE DNA TOPOISOMERASE-II-MEDIATED CLEAVAGE OF THE LONG TERMINAL REPEAT OF DROSOPHILA 1731 RETROTRANSPOSON

The interaction of DNA topoisomerase II with the long terminal repeat (LTR) of the Drosophila melanogaster 1731 retrotransposon was studied. The covalent binding of topoisomerase II to the LTR was strongly stim ulated by different inhibitors of the enzyme toxin-9-(4,6-O-2-ethylide ne-beta-D-glucopyranoside (VP-16), 4'-(9-acridinylamino)methanesulfon- m-anisidine) (m-AMSA) and an ellipticine derivative. Enzyme-mediated D NA cleavage could be observed in the absence of inhibitors and was sti mulated in their presence. Cleavage occurred predominantly at sites lo cated within or at the boundary of alternating purine/pyrimidine tract s in agreement with previous observations [Spitzner, J. R., Chung, I. K. & Muller, M. T. (1990) Eukaryotic topoisomerase II preferentially c leaves alternating purine-pyrimidine repeats, Nucleic Acids Res. 18, 1 -11]. In addition, all of the cleavage sites observed in the absence o f inhibitor were located in the U3 region of die LTR. The site specifi city of drug-induced cleavage was studied and the conformity of the cl eavage sites with previously established consensus sequences was exami ned. Our results suggest that DNA topoisomerase II, through its abilit y to alter the degree of DNA supercoiling, might be involved in the co ntrol of different functions of die LTR.