FIG. 6.

The sGP₃ of the IAF-Klop strain of PRRSV is released from the cell as a membrane-free form. (A) Sensitivity of sGP₃ to trypsin digestion in the presence or absence of detergent. Prior to radioimmunoprecipitation of sGP₃, the culture medium of 293 cells infected with AdCMV5/ORF3 was supplemented with trypsin, NP-40, and/or trypsin inhibitor as indicated in Materials and Methods. The culture medium was allowed to stand for 30 min at 25°C and was then analyzed by radioimmunoprecipitation. (B) In a second experiment, Triton X-100 was added to the culture medium, which was next subjected to centrifugation at 200,000 × g for 1 to 2 h. The resulting pellet (P) and supernatant (S) fractions were assessed by radioimmunoprecipitation for the presence of sGP₃. In both experiments, protein bands between 5 and 30 kDa were not revealed (data not shown). Positions and sizes of ¹⁴C-radiolabelled marker proteins are indicated between the two gels.