Pellet nuclei by centrifugation at 1500 xg for 10 min. Transfer to an eppendorf microfuge tube. Add an equal volume of 1M NaCl, vortex, leave on ice for 30-60 min. Spin in ultrcentrifuge at 100,000 xg for 1 hr. Alternatively, you may be able to spin in the cold in a microfuge at 12-15,000 xg for 15 min.
Ultracentrifugation is best, however.
The supernatant will contain topo I and II activities.