FIGURE 4.

Residues in an MV H N-terminal domain are determinants for F specificity. A, quantification of fusion activity upon activation of CDV F-Lederle or MV F with CDV H, MV H, or an MV/CDV H chimera specified in the schematic below the graph. The activity was determined as outlined before (Fig. 1A), and the values are expressed as a percentage of activity observed for either CDV F-Lederle or MV F co-expressed with CDV H. The averages of three independent experiments ± S.D. and the extent of differential triggering are shown. Stalk, membrane-proximal part of the H ectodomain (up to residue 139); TM, transmembrane domain; CT, cytosolic tail. B, microphotographs of Vero-dogSLAM cells co-transfected with the constructs outlined in A. The pictures were taken 9.5 h post-transfection at a magnification of 200×. Mock transfected cells received only F-encoding plasmid.