FIG. 5.

Coexpression of S protein is required for protease protection of the L protein. Microsomal membranes were prepared from LMH cells transfected with a plasmid, L⁺S⁻, which has an altered start site for S and is defective for S production, or cotransfected with a plasmid, L⁻S⁺, containing a stop codon (G1165A) in the pre-S domain and defective in L synthesis, at L/S ratios of 5:1, 1:1, and 1:5. Each sample was divided into three aliquots, which were subjected to digestion with trypsin, with or without NP-40, or left untreated as denoted above each lane, and protease protection was analyzed by Western blotting with an anti-pre-S antiserum.