FIG. 6.

B5R mutant viruses release enhanced levels of virus into the culture supernatant. RK₁₃ cells were infected with the indicated viruses at 1 PFU/cell. At 24 hpi, the culture supernatant was collected and clarified by low-speed centrifugation (2,000 rpm in a Beckman GPR benchtop centrifuge for 10 min), and then the infectious virus present in this fraction was determined by duplicate plaque assay on monolayers of BS-C-1 cells. The infected cells were scraped from the monolayer into PBS, combined with the pellets derived from clarification of the culture supernatant, pelleted as described above, and lysed by freeze-thawing and sonication. Infectious virus present in the sonicate was determined by plaque assay on BS-C-1 cells. Plaque assays were stained between 48 and 120 hpi. (A) Data are presented as the titer of virus present in cells (hatched bars) or the culture supernatant (stippled bars) ± SEM (n = 3); (B) data are expressed as the percentage of total infectious virus that was released into the culture supernatant ± SEM (n = 3).