Mutational Analysis of the Herpes Simplex Virus Type 1 ICP0 C3HC4 Zinc Ring Finger Reveals a Requirement for ICP0 in the Expression of the Essential a27 Gene

The herpes simplex virus type 1 (HSV-1) immediate-early (IE) protein ICP0 has been implicated in the regula-tion of viral gene expression and the reactivation of latent HSV-1. Evidence demonstrates that ICP0 is an activator of viral gene expression yet does not distinguish between a direct or indirect role in this process. To further our understanding of the function of ICP0 in the context of the virus life cycle, site-directed mutagen-esis of the consensus C3HC4 zinc finger domain was performed, and the effects of these mutations on the growth and replication of HSV-1 were assessed. We demonstrate that alteration of any of the consensus C3HC4 cysteine or histidine residues within this domain abolishes ICP0-mediated transactivation, alters the intranuclear localization of ICP0, and significantly increases its stability. These mutations result in severe defects in the growth and DNA replication of recombinant herpesviruses and in their ability to initiate lytic infections at low multiplicities of infection. These viruses, at low multiplicities of infection, synthesize wild-type levels of the IE proteins ICP0 and ICP4 at early times postinfection yet exhibit significant decreases in the synthesis of the essential IE protein ICP27. These findings reveal a role for ICP0 in the expression of ICP27 and suggest that the multiplicity-dependent growth of a0 mutant viruses results partially from reduced levels of ICP27. Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) infections proceed from a primary lytic infection in the periph