FIG. 3.

Changing the 3B-3C cleavage site from GG to EG restores infectivity. (A) Infectious center assay for EG mutant and WT PV RNA. HeLa cells were transfected with in vitro-transcribed EG mutant or WT PV RNA, diluted, added to HeLa cell monolayers, overlaid with agarose, and held at 37°C for 2 days, at which time the agarose overlay was removed and cells were stained with crystal violet. (B) Quantitation of data shown in panel A. The specific infectivities for WT and EG mutant RNA are 68,000 ± 10,000 and 14,000 ± 1,000 PFU/μg RNA, respectively.