Fig. 4.

Electron micrographs of COS-1 cells transfected with pCAG-CprME. The COS-1 cells were transfected with pCAG-CprME or optimal medium as negative control. The cells were then trypsinized at 24 and 72 hours post-transfection (hpt), centrifuged, and after supernatant removal they were resuspended in a fixative solution (2.5% v/v glutaraldehyde in 0.1 M phosphate buffer [pH 7.4]), and sent for electron microscopy examination. (A and E) Spherical tick-borne encephalitis virus viral-like particles (TBE VLP) (50 nm in diameter) were observed in the lumen of membrane-bound vesicles at (A and B) 24 hpt and (C through E) also at 72 hpt in pCAG-CprME-transfected cells. (E) Highly proliferating rough endoplasmic reticulum (rER) (indicated by star) was observed in the pCAG-CprME-transfected cells. (F and G) The COS-1 cells were transfected with optimal medium as negative control and examined by electron microscopy at 72 hpt to compare with pCAG-CprME-transfected cells. The VLPs and membrane-bound vesicles are indicated by black arrow and triangles, respectively. The scale bar for each image is also shown. A possible premature TBE VLP composed of CprME is also indicated by a white arrow. Nu = nucleus; Mito = mitochondria; GA = Golgi apparatus; CI = clathrin-coated vesicle.