FIG. 3.

In PV-infected cells, formation of PV vesicles occurs at the ER. (a) Isosurface picture of a part of a cell labeled for p63 (green) and 2B (red). Colocalization of the markers is restricted to flat yellow patches (arrowheads), representing the sites of association of 2B marker protein with the ER and to collar-like transition sites between ER and vesicles (arrow; see also panel c). The dashed line confines the area shown in panel c. Bar, 1 μm. (b) Higher-magnification isosurface view showing part of a cell labeled for MERG, i.e., a series of ER-resident proteins (green) and 2B (red). Their colocalization (yellow) with 2B is in transition sites only, as for p63 and 2B in panel a. Bar, 0.5 μm (in foreground). (c) Consecutive optical sections through the zone of the cell outlined in Fig. 3a (dashed line). By following an emerging vesicle through the sections (arrows), it can be seen that the antigens p63 (green) and PV 2B (red) colocalize (yellow) to form a ring-like structure which evolves into a red vesicle. The thickness of an optical section is 70 nm. Bar, 1 μm. (d) A cluster of 2B-positive vesicles (red) is emerging from the ER labeled for p63 (green). Bar, 200 nm (in foreground). (e) EM picture of a section through a comparable cluster of vesicles (arrowheads) associated with the ER (arrow), partially carrying ribosomes. The vesicles are of similar size and arrangement as the vesicles found by confocal microscopy. Bar, 200 nm. (f) Isosurface picture showing anti-Sec31-labeled vesicles (red) which are budding from the ER (green) (p63) in a PV-infected cell. Bar, 2 μm (in foreground). (g and h) Vesicles were labeled with anti-2B Ab (red) and either with anti-Sec13 (g) or anti-Sec31 (h). Both COPII components largely colocalize (yellow) with 2B. Bars, 2 μm (in foreground).