Figure 6. SLSs within ICP0 regulate its ability to complement and reactivate mutant HSV-1 viruses in cell culture.

(A) As in Figure 3A. (B) Complementation of ICP0-null mutant HSV-1 plaque formation by prior induction of expression of various N-terminal fragments of ICP0 (as depicted in A) and full-length ICP0 carrying individual or combined SLS mutations in the inducible cell line system. The titre of a mutant virus stock was determined in each cell line and plotted with respect to that in cells expressing wt ICP0. Means and standard deviations of two to seven independent determinations are presented. (C) Analysis of ICP0 induced reactivation of gene expression from quiescent HSV-1 genomes. Cells were infected with multiply defective HSV-1 mutant in1374 to establish quiescently infected cultures, then 24 h later ICP0 expression was induced with doxycycline. Reactivation was assessed the following day by staining for β-galactosidase expression from the marker gene in the in1374 genome. The proportion of reactivated cells in each cell line was expressed as a percentage of that in cells expressing wt ICP0 following determination of positive cell numbers in three high magnification views of each sample. Means and standard deviations are presented.