Figure 3. Production of cytopathic effect and proteolytic cleavage of the F0 proteins of parental and F protein cleavage site mutant APMV-4 viruses.

(A) DF1 cells in six-well plates were infected with the indicated viruses at a multiplicity of infection (MOI) of 0.1 PFU/cell and incubated for 72 h. (B) The viral plaques in the infected cells were visualized by immunoperoxidase staining using antiserum against the N protein of APMV-4; viral antigen is stained red. (C) Proteolytic cleavage of the F0 proteins of parental and mutant viruses in infected DF1 cells was analyzed by Western blot (I) in triplicate. The positions of the precursor protein F0 and the cleavage product F1 are indicated. The relative levels of the F0 and F1 proteins in the Western blot images were measured by Bio-Rad Gel Image analysis, and the efficiency of cleavage was determined by dividing the amount of F1 by the amount of F1 plus F0 (II).