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. 1998 Nov 10;95(23):13531–13536. doi: 10.1073/pnas.95.23.13531

Figure 5.

Figure 5

Results of competition experiments between psorospermin and the topoisomerase II inhibitors m-AMSA and etoposide. (A) The Drosophila topoisomerase II–DNA complex was formed as described in Materials and Methods in the presence of various amounts of m-AMSA and etoposide. Psorospermin (10 μM) then was added to the reaction mixture, and the reaction continued for another 5 min followed by heat strand breakage (8). Lanes 1 and 2 are control DNA without and with heat treatment, respectively. Lanes 3 and 4 contain the Maxam–Gilbert sequencing reactions for AG and TC. Lane 5 contains DNA and psorospermin only. Lane 6 contains DNA, psorospermin, and topoisomerase II without inhibitor. Lanes 7–11 and 12–16 contain 5, 10, 25, 50, and 100 μM m-AMSA and etoposide, respectively. (B) Strand breakage products indicated by the arrowhead in A were quantitated using a PhosphorImager and analyzed by using imagequant 4.1 software (Molecular Dynamics). The intensity of the DNA cleavage produced by psorospermin was determined from the volume of the bands (indicated by the arrowhead in A) normalized by the total radioactivity in each lane.