Fig 4. Mutations R667A, T678S and R797N are compatible with robust S protein-driven cell entry.

(A) 293T cells transfected to express MLV particles pseudotyped with SARS S wt or the indicated SARS S mutants and the corresponding supernatants were analyzed for expression of S protein (employing anti-V5 antibody) and MLV capsid protein (employing anti-p30 antibody) by Western blot. Cells transfected to express S protein alone or transfected with empty plasmid were used as controls. Similar results were obtained in two independent experiments. (B) 293T target cells transfected with empty plasmid (control) or ACE2 plasmid were transduced with equal volumes of pseudotypes bearing the indicated viral glycoproteins. Transduction efficiency was quantified by measuring luciferase activities in cell lysates. Results were normalized for SARS S-driven transduction of ACE2 expressing cells, which was set as 1-fold. The average of three to eight independent experiments is shown. Error bars indicate standard error of the mean (SEM).