FIG. 4.

Syncytium assay for cell-cell fusion. wt SV5 F (A) and HeV F (B) and the CBF₂ mutants were expressed in BHK cells with or without their attachment proteins by use of the pCAGGS vector expression system. Fifteen hours (SV5 F) or 29 h (HeV F) posttransfection, pictures were taken of cells at ×100 magnification and examined for the formation of multinucleated giant cells termed syncytia.