FIG. 9.

E1 trimer formation in wt and D188K mutant SFV. (A) Radiolabeled viruses were mixed with liposomes and treated at the indicated pH for 5 min at 20°C. Aliquots of the samples were analyzed for SDS-resistant-trimer formation, trypsin-resistant-trimer formation, or reactivity with the acid conformation-specific MAb E1a-1, as detailed in Fig. 4 and Materials and Methods. Shown are the averages of two experiments; with the bars representing the range. Recovery of the trimer by immunoprecipitation with MAb E1a-1 is less efficient than its detection by SDS or trypsin resistance. (B) Interaction of viral E1 with exogenous DIII protein. Radiolabeled wt or D188K mutant SFV was prebound to BHK cells on ice and treated for 1 min at 37°C with buffer at the indicated pH and containing 2 μM His-DIIIS protein. The cells were lysed, and aliquots of the samples were immunoprecipitated with a polyclonal antibody to E1/E2 to recover total E1, an antibody to the His tag (His), and an irrelevant MAb (ns). The data shown are the averages and standard deviations of three independent experiments.