Viral proteins in mFIPV-infected LR7 cells (A), in r-wtFIPV infected FCWF cells (B), and in FIPVΔ7b-infected FCWF cells (C). In panel A, analyses were done with LR7 cells infected with mFIPV and, for comparison, with MHV-infected LR7 cells and FIPV-infected FCWF cells. In panel B, analyses were done with r-wtFIPV-infected FCWF cells and, for comparison, with FIPV-infected FCWF cells, and in panel C, analyses were done with FIPVΔ7b-infected FCWF cells and, for comparison, with FIPV- and r-wtFIPV-infected FCWF cells. In all cases the cells were labeled for 2 h with 35S-labeled amino acids. Immunoprecipitations were performed on aliquots of cleared lysates of these cells by using the following antibodies: ascitic fluid G73 (αFIPV) from an FIPV-infected cat; K134 (αMHV), a rabbit serum raised against purified MHV strain A59; WA3.10 (αSm), an MAb against an epitope present in the MHV S ectodomain; and 23F4.5 (αSf), an MAb against an epitope in the FIPV S ectodomain. All samples were heated at 95°C prior to electrophoresis, except for the sample analyzed in panel A, lane 4, which was run without heating and analyzed in sodium dodecyl sulfate-12.5% polyacrylamide gels. The positions of the S, N, M, and 7b (C) proteins are indicated at the left for MHV and at the right for FIPV.