FIG. 5.

MVs activated by papain digestion enter cells through a low-pH-dependent pathway. Purified WRvFire MVs were incubated with 50 μg/ml papain for 30 min at 37°C (PAPAIN), or mock treated (MOCK PAPAIN), quenched in an excess of EMEM plus 2.5% FBS, and then overlaid onto BS-C-1 monolayers that had been pretreated with bafilomycin A1 (A) or monensin (B) for 1 h at 37°C. RLU, relative light units. Virus adsorption was allowed to continue for 1 h at 4°C before the cell monolayers were washed and incubated in the presence of inhibitor for an additional 1 h at 37°C. The cells were then lysed and assayed for Luc activity. As controls, untreated WRvFire MVs were adsorbed to BS-C-1 monolayers pretreated with bafilomycin A1 or monensin and induced to fuse at the plasma membrane by transient incubation with pH 5 buffer (pH 5 POST) or allowed to enter via a low-pH endocytic pathway by mock treatment with pH 7.4 buffer (pH 7.4 POST).