FIG. 7.

Comparison of the extent of fusion promoted by wt F and L289A-F expressed with HN proteins carrying mutations in the NA active site that render the protein deficient in attachment function. Proteins are expressed in BHK cells driven by the vaccinia virus-T7 RNA polymerase expression system. The extent of fusion was quantitated with the content-mixing fusion assay and expressed as the percentage of that obtained with wt HN and wt F. Error bars show the standard deviation from at least four independent determinations.