Analysis by Western blotting of cell extracts and supernatants obtained at different times post-infection from permissive chicken DF-1 cells infected with MVA-S(3P) showed only cell-associated S protein that migrated with a size about 180 kDa, similar to the native S (Figure 1B), and as expected for a full-length glycosylated S protein containing the transmembrane domain. This evidence concerns the gene PROS1 and infection.