Fig. 3.
SARS-CoV S cleavage by trypsin facilitates entry into Calu3 cells. (A) SARS and HCoV-229E pps were treated with trypsin. S proteins on pps were analyzed by Western blot. Uncleaved (Sunc) and cleaved (S2) positions are indicated. The numbers at the left indicate molecular mass in kilodaltons. (B) Calu3 cells were incubated with trypsin pretreated pps. Virus entry was quantified by measuring luciferase levels at 48-h posttransduction. Error bars present SD from the mean (n = 4). Statistical significance was assessed by Student's t test. ‡P < 0.001.