Characterization of the role of RNA for the VP1-VP3 interaction. (A) Cultures of BSC-1 cells were infected with VT7/VP1 or VT7/VP3, metabolically labeled with [35S]methionine, harvested at 20 h p.i., and used to prepare protein extracts. The extracts were either untreated (−) or treated with 0.2 or 1 mg of RNase A/ml. Thereafter, samples were mixed, and the VP1-VP3 interaction was allowed to proceed ON at 4°C. After incubation, samples were subjected to IP with anti-VP3 rabbit antiserum. The resulting samples were subjected to SDS-PAGE and electroblotted onto nitrocellulose. The filters were subjected to autoradiography. (B) Western blot analysis of the immunoprecipitated products. After autoradiography, filters were excised in half. The upper and lower halves were incubated with anti-VP1 and anti-VP3 sera, respectively. After incubation with the corresponding antisera, filters were developed by the addition of horseradish peroxidase-conjugated goat anti-rabbit immunoglobulin. In both cases, the signal was detected by enhanced chemiluminescence. In each panel, the positions of standard protein molecular size (in kilodaltons) markers are indicated on the left (Mw). Arrowheads in both panels indicate the positions of bands corresponding to the VP1 and VP3 polypeptides.