FIG. 7.

CsCl density gradient analysis of IMV and enveloped viruses produced by vF12L, vΔF12L and vF12L-rev. RK₁₃ cells were infected with the indicated viruses at 10 PFU per cell and labeled with 100 μCi of [³H]thymidine (Amersham) from 1.75 h p.i. At 24 h p.i., the virus in the infected cells (A) or culture supernatant (B) was purified by CsCl density gradient centrifugation as described previously (36). The density of the fractions was determined by refractometry. The infectious virus present in peak fractions corresponding to IMV or EEV was titrated by plaque assay on BS-C-1 cells, and the amount of radioactivity in these fractions was determined by scintillation counting. These values are displayed underneath the graphs, and the relative differences between the deletion mutant and control viruses are displayed.