FIG. 4.

Cleavage of SARS S proteins during virus entry. HIV-SARS S pseudoviruses were spinoculated onto target hACE2-293 cells transfected 2 days earlier with the pCAGGS empty vector or pCAGGS-TMPRSS2 (1 μg per 10⁶ cells, in duplicate). After spinoculation, cells were incubated at 37°C for 1 h to allow the cleavage of S proteins by cell surface TMPRSS2. After removal of unbound pseudovirions and washing, cells were lysed and evaluated by IB for S proteins using anti-C9 tag antibody. The values to the left are molecular sizes in kilodaltons.