FIG. 4.
Immunoblot analysis of Topo I-DNA covalent complexes stabilized by Topo I inhibitor in HeLa cell nuclei. HeLa cell nuclei (5 × 106) were incubated for 3 h at 37°C in the presence or absence of compounds (5 μM). The lysates obtained were applied to a CsCl gradient and centrifuged overnight. Twelve fractions were collected and analyzed by slot blot assay. Fractions 1 to 4 contained free Topo I. Topo I/DNA covalent complexes were detected in fractions 8 to 11. Results are representative of three independent experiments.