FIG. 7.
Growth of cleavage site and proteinase combination mutants. DBT cells were infected at an MOI of 1 PFU/cell with the indicated viruses as described in Materials and Methods. At the times indicated postinfection, aliquots of medium were obtained, and titers were determined by plaque assay on DBT cells. Data points are the means of two samples each of two concurrent independent replicate experiments for each virus. Growth of VURG19 was at or below the level of detection, but an estimate of growth is illustrated by a dotted line for comparison.