NiV G stalk domain determines the oligomerization state of the chimeric binding proteins. Monolayers of cells coexpressing NiV F and either the indicated chimeric glycoproteins, NDV HN, or NiV G were incubated in a medium supplemented with 35S-labeled amino acids. The cells were lysed, and the envelope glycoproteins were immunoprecipitated and subjected to SDS-PAGE under nonreducing (A and B) or reducing (C and D) conditions. Representative autoradiography shows the oligomeric state (A) and the level of protein expression (C) of the receptor binding glycoproteins, immunoprecipitated with anti-NDV HN antibodies. Note that monoclonal antibodies against NiV G were used in the lane marked NiV G. In panels B and D, the same samples were immunoprecipitated with anti-NiV F antibodies showing similar F expression (B) and processing (D) regardless of the coexpressed viral glycoproteins.