FIG 1.

The IBV S protein is aberrantly processed in virions from IBV EG3-infected cells. (A) Cartoon of IBV Beaudette S showing the cleavage sites. The signal sequence (ss), fusion peptide (FP), and transmembrane domain (TMD) are indicated. (B) Representative blot of virions purified from the supernatants of WT IBV- or IBV EG3-infected Vero cells by concentration through a sucrose cushion. Pellets were electrophoresed on NuPAGE 4-to-12% gradient gels and after transfer to PVDF membranes were probed with mouse anti-S1 and rabbit anti-S2, followed by IRDye 800CW donkey anti-mouse IgG and IRDye 680CW donkey anti-rabbit IgG. The left panel is a merge of the 800-nm and 680-nm wavelengths of the Li-Cor image showing that S1 and S2 essentially comigrate on these gradient gels. The middle and right panels show the signal for the S1-specific mouse monoclonal 3C7B8 and the rabbit anti-S C terminus antibodies (Ab), respectively. The cleavage products are indicated, as are the positions of the molecular weight markers (in kilodaltons). (C) Quantification showing the fraction of total S for each S1 fragment (top graph) or S2 fragment (bottom graph). Error bars indicate standard deviations (SD) (n = 4 [S2 antibody] or 3 [S1 antibody]). A paired t test was performed in GraphPad Prism, with a P value of <0.05 (*) where indicated. All other pairs were not statistically significant.