FIG. 4.

Binding of BPV1 virions containing L2 deletion mutants to the cell surface. L1 was coexpressed with recombinant SFV with either wild-type L2, L2Δ2–9, or L2Δ461–49 in BPHE-1 cells. Upon cell lysis by sonication, virions were separated from pentamers and empty VLPs by rate zonal centrifugation through a 20 to 40% (wt/vol) sucrose gradient for 90 min at 160,000 × g at 4°C. L1/L2 (A and E, lane 1), L1/L2Δ2–9 (B and E, lane 2), and L1/L2Δ461–49 (C and E, lane 3) virion preparations and buffer alone (D) were incubated at equivalent concentrations for 1 h at 4°C with mouse C127C cells. The cells were washed, and bound virions were detected by indirect immunofluorescence with monoclonal antibody 5B6 to L1. The quality and quantity of virion preparations was estimated by Western blot analysis with rabbit antiserum to BPV1 L1/L2 VLPs (E). In panel E, molecular masses are given to the left in kilodaltons.