FIG. 4.
The disulfide-linked form of the T216C-D230C-mutated NDV-L HN is expressed at the cell surface. Cells were transfected as indicated and labeled for 3 h with 300 μCi of Expre35S[35S] cysteine-methionine labeling mix. The cells were then placed on ice and washed twice with ice-cold phosphate-buffered saline containing 0.1 mM CaCl2 and 1 mM MgCl2 (PBS-CM). The monolayers were incubated for 1 h in the cold with 2 ml of a mixture of anti-HN hybridoma supernatants, washed five times with cold PBS-CM, and lysed, and HN was immunoprecipitated as described above, followed by SDS-PAGE without BME. The numbers in the lane marked M indicate the migration rates of markers in kilodaltons.