Immunoprecipitation of labeled membrane proteins. Proteins from C6/36 cell apical surfaces radiolabeled with 125I (lane 1) were immunoprecipitated with polyclonal anti-MG (lane 2) or anti-membrane (lane 3 and 4) and separated by 10% SDS-PAGE. The molecular weights of the immunoprecipitated proteins are shown on the left side. A negative control using an unrelated antibody (anti-actin) is shown in lane 5. Labeled apical cell surface proteins recognized by DEN1 (lane 7), DEN2 (lane 8), DEN3 (lane 9) and DEN4 (lane 10) were immunoprecipitated with specific anti-DENV as described in the methods section. A control without DEN virus was included (lane 6). 125I-labeled proteins immunoprecipitated by anti-EP were used as a positive control (lane 11). All proteins were separated by 10% SDS-PAGE and labeled proteins were detected by autoradiography. The molecular weights of these proteins are shown on the right side. Molecular weight markers are shown on the left side.