FIG. 7.

Mutations blocking cleavage of the I or C site, or both, reduce virus titer. Plaque assays were done for samples taken over a 9-day period following infection with the Wt or mutant viruses (I⁻, C⁻, and I⁻/C⁻), as described in Results and Materials and Methods. Shown here are logarithmic (A) and arithmetic (B) plots of the data. Panel B inset shows fluorescence (i.e., GFP reporter expressed from viral genome) images of representative fields from the infected cultures 3 days after addition of virus and reveals comparatively fewer GFP-expressing cells (i.e., infected) in the culture infected with wild-type virus. §, standard deviations (indicated by vertical bars at each data point) for the titers of day 9 I⁻ virus [±(0.8 × 10⁶)] and day 8 Wt virus [±(0.4 × 10⁶)] were higher than those for all other determinations and are not shown because they obscure other data.