FIG. 3.

Syncytium formation in BHK cells induced by wt F and L289A-F with and without HN expressed by two different transient expression systems. In the top row, the indicated proteins are expressed from the pBSK vector driven by the vaccinia virus-T7 RNA polymerase expression system. In the bottom row, the indicated proteins are expressed from the pCAGGS vector driven by the chicken β-actin promoter. The monolayers were fixed with methanol and stained with Giemsa stain at either 22 h (vaccinia virus-T7) or 18 h (pCAGGS) posttransfection.