Electron micrographs of ultrathin sections of BHK-21 cells electroporated with SFV/Dj (A and B) or SFV/Dj-C173 (C) RNA. The large arrow in panel A indicates ER, revealing a dilated lumen and convoluted membranes, the arrowheads in panel B indicate virus-like particles budding from these convoluted membranes towards the ER lumen, and the arrows in panel C indicate normal, homogeneously distributed ER structures throughout the cytoplasm. Bars, 1 μm (A), 100 nm (B), and 200 nm (C).