FIG. 6.
(A) Diagram of the vA9i genome. The expression of the A9L ORF is under the control of the T7 promoter and is IPTG inducible. Abbreviations: PT7, T7 promoter; P11, vaccinia virus late promoter; PE/L, vaccinia early/late promoter; TK, thymidine kinase locus; T7 pol, T7 polymerase ORF; GUS, β-glucuronidase ORF; lacI, E. coli lac repressor ORF; lacO, E. coli lac operator element. (B) Effect of IPTG on formation of vA9i plaques. Monolayers of BS-C-1 cells were infected with either vT7lacOI or vA9i in the presence or absence of 100 μM IPTG as indicated. At 48 h after infection, plaques were visualized by staining with crystal violet. (C) Effect of IPTG on virus yields over time. BS-C-1 cells were infected with vaccinia virus T7LacOI or vA9i at a multiplicity of 5 in the presence or absence of 100 μM IPTG and were harvested at 6, 12, 24, and 48 h after infection. Virus titers for each sample were determined by plaque assay on BS-C-1 cells in the presence of IPTG.