buffer and resuspended in sonication buffer (50 mM Tris-HC1, 2 mM EDTA, and 0.2% PD, pH 8.0) at a concentration of 0.1 gram of wet cell mass per ml. Cells were then broken by sonication (four 30 sec. bursts with 1 min. cooling intervals on ice) using a VirSonic 300 sonicator (The Virtis Company, Inc., Gardiner, NY) with a 10 mm diameter disruptor horn and an output setting of 10. After sonication, the crude cell extract was diluted with an equal amount of B-PER II supplemented with 400 mM NaCl and 20 mM MgC12 and then incubated at 4°C for 30 minutes on a rotary shaker set at 18 RPM. Unlysed cells and cell debris were removed by centrifugation at 12,000 x g for 10 min. and the resulting supernatant was then subjected to high-speed centrifugation (Beckman SW-27 rotor, 49,000 x g, 90 min.). The pellet was resuspended in 5 ml of TEMP buffer (50 mM Tris-HC1, 1 mM EDTA, 10 mM MgC12, 0.2% PD, pH 8.0) and then clarified by low-speed centrifugation (12,000 x g, 10 min.). The clarified preparation was layered over two 35 ml, 35-65%, continuous sucrose gradients in 38.5 ml tubes and centrifuged for 12 hr (Beckman SW-27 rotor, 104,000 x g). The polyhedral organelles formed a white translucent band about 2/3 of the way down the centrifuge tube whereas membrane fragments and amorphous debris formed an opaque tan band below. The fraction containing the polyhedra was collected from each gradient with a plastic pipette, diluted to 38.5 ml with TEMP buffer, and centrifuged at 52,000 x g for 90 min. The pellets were resuspended in 1 ml of TEMP buffer and clarified by centrifugation for 10 min at 4,000 x g using an Eppendorf 5415C microcentrifuge. The supernatant containing the purified organelles was carefully removed and stored at 4°C prior to analysis.