FIG. 2.

Immunofluorescence microscopy analysis showing the intracellular distribution of the SARS-CoV nsp13 helicase in infected Vero E6 cells. Cells were fixed at 6 h postinfection (A, top row) or 9 h postinfection (A [bottom row], B, and C) and analyzed with a conventional fluorescence microscope (A) or laser scanning confocal microscope (B and C). The SARS-CoV nsp13 staining developed from a punctatedispersed pattern at 6 h postinfection to a large, mainly perinuclear staining at 9 h postinfection. Part of the nsp13 signal overlapped the labeling for the ECFP-ER and PDI marker proteins used in this study, whereas no colocalization with a Golgi marker protein (EGFP-Golgi) was observed. Bar, 20 μm. (A) Prior to infection, cell cultures were transfected with an expression plasmid encoding endoplasmic reticulum-targeted ECFP. Part of the cells remained untransfected or uninfected, explaining the cells positive for nsp13 or the marker protein only. (B) Nontransfected cells were infected with SARS-CoV at a multiplicity of infection of 1 and used for double labeling with antisera recognizing nsp13 and the cellular protein PDI, a resident protein of the endoplasmic reticulum and intermediate compartment. (C) Prior to infection, cell cultures were transfected with an expression plasmid encoding Golgi complex-targeted EGFP.