The connecting region from NiV G stalk cannot be substituted by the NDV HN 110-124 or 120-124 stalk region. 293T cells coexpressing NiV F with the NiV-NDV chimeric binding protein were allowed to bind to receptor-bearing RBCs at 4°C in the presence of zanamivir. Zanamivir was added to activate NDV HN site II. Unbound RBCs were then washed, and standard medium with zanamivir, for the activation of binding site II, was added at 37°C for 120 min. The values on the y axis reflect quantification of RBCs that were (i) released (□), (ii) bound (▩), or (iii) fused (■). The values are means (± the standard errors) of results from two representative experiments.