FIG. 4.
Immunoprecipitation assays indicating that C303G and C320G NAs do not fold normally at 39.5°C. (A) Immunoprecipitation of NA proteins. (B) Immunoprecipitation of viral structural proteins HA, NP, and M1. Immunoprecipitations were performed on lysates of MDCK cells infected with the indicated viruses and incubated at the indicated temperatures. The cultures were labeled with [35S]methionine-[35S]cysteine for 1 h and chased with unlabeled medium for 1 h, beginning 12 h postinfection. Immunoprecipitation of NA was performed with a mixture of two monoclonal antibodies, 3C8 and 10C9 (43). Immunoprecipitations of HA, NP, and M1 were performed with a polyclonal anti-WSN virus antiserum, 8236.