FIG. 2.
The spike protein of FCoV UCD, but not that of FCoV UCD1, is cleaved by a furin-like protease. OST7-1 cells infected with vaccinia virus vTF7-3 were transfected with plasmids carrying either the UCD or UCD1 spike gene under the control of bacteriophage T7 transcription regulatory elements. The cells were pulse-labeled with 35S-amino acids for 1 h and subsequently chased for 0, 30, 60, 120, or 180 min. Where indicated by a plus, the furin inhibitor dec-RVKR-cmk (75 μM) (left panel) or the mannosidase I inhibitor DMJ (1 mM) (right panel) was added to the culture media and kept present throughout the experiment. Spike cleavages of the wild-type (WT) and mutant (MUT) UCD and UCD1 proteins were also compared (see text for details). The cells were lysed and processed for immunoprecipitation using FCoV RM antiserum. The immunoprecipitates were analyzed by SDS-PAGE. The position of a molecular weight marker (Mr) is shown on the left side of the panels. The asterisks indicate the positions of the mature UCD1 spike protein. The arrows indicate the positions of the S1 cleavage products. Only the relevant portion of the gel is shown.