An earlier report showed that the expression of viral genes by a herpes simplex virus 1 mutant [HSV-1(vCPc0)] in which the wild-type,
spliced gene encoding infected-cell
protein no. 0 (ICP0) was replaced by a
cDNA copy is dependent on both the cell type and multiplicity of
infection. At low multiplicities of
infection, viral gene expression in rabbit skin cells was delayed by many hours, although ultimately virus yield was comparable to that of the wild-type virus. This defect was rescued by replacement of the
cDNA copy with the wild-type gene. To test the hypothesis that the delay reflected a dysfunction of ICP0 in altering the structure of host
protein-viral DNA complexes, we examined the state of
histone deacetylases (HDACs) (HDAC1, HDAC2, and HDAC3). We report the following. (i) HDAC1 and HDAC2, but not HDAC3, were modified in infected cells. The modification was mediated by the
viral protein kinase U(S)3 and occurred between 3 and 6 h after
infection with wild-type virus but was delayed in rabbit skin cells infected with HSV-1(vCPc0) mutant, concordant with a delay in the expression of viral genes. (ii) Pretreatment of rabbit skin cells with inhibitors of HDAC activity (e.g.,
sodium butyrate,
Helminthosporium carbonum toxin, or
trichostatin A) accelerated the expression of HSV-1(vCPc0) but not that of wild-type virus. We conclude the following. (i) In the interval in which HSV-1(vCPc0)
DNA is silent, its
DNA is in
chromatin-like structures amenable to modification by inhibitors of
histone deacetylases. (ii) Expression of wild-type virus genes in these cells precluded the formation of
DNA-
protein structures that would be affected by either the HDACs or their inhibitors. (iii) Since the defect in HSV-1(vCPc0) maps to ICP0, the results suggest that this
protein initiates the process of divestiture of
viral DNA from tight
chromatin structures but could be replaced by other
viral proteins in cells infected with a large number of virions.