FIG. 2.

Expression of S protein constructs. (A) Cell surface expression of S mutants in 293T cells. Cells were transfected with DNA encoding either full-length S (wt) or cytoplasmically truncated S protein (CΔ8 to CΔ39). Mock-transfected 293T cells (thin line) were used as a negative control. FACS analysis was performed with SARS antiserum (1:50) and anti-human IgG antibody conjugated with phycoerythrin. (B) Immunoblot of transfected 293T cells (left panel) and purified viral particles (right panel). At 48 h after transfection with HA-tagged CΔ19 S expression construct, cells were lysed either directly (CΔ19-HA) or after being detached from the wells with trypsin-EDTA (CΔ19-HA/Trypsin) and subjected to Western blot analysis with monoclonal anti-HA antibody. Lysates of mock-transfected 293T cells were used as a control (mock). Viral particles with or without trypsin treatment were analyzed likewise. Supernatants produced in the absence of a viral envelope (no env) served as a control. Molecular size standards (in kilodaltons) are indicated.