Figure 2.

Establishment of two quantitative entry assays. (A) [³⁵S]methionine-labeled and -purified IMV or EEV (indicated) were bound and allowed to enter HeLa cells as described in Materials and Methods. At the indicated times, the cells were digested for 60 min on ice with 0.2 mg/ml of trypsin, and penetrated virus was separated from unpenetrated virus by pelleting the cells. The percentage of entry was calculated by dividing the cell-associated counts by the total counts (the addition of cell-associated and non-cell–associated cpm). The values are the average of duplicates. (B) Purified IMV or EEV preparations were bound for 60 min at RT to monolayers of HeLa cells at different MOIs. The cells were transferred to 37°C and were fixed after incubation at this temperature for the indicated times. Entry was determined by counting the average amount of intracellular cores per cell by immunofluorescence in 30 HeLa cells.