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 ALPHA-27 GENE

The herpes simplex virus type 1 (HSV-1) immediate-early (IE) protein I CP0 has been implicated in the regulation 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 understandi ng of the function of ICP0 in the context of the virus life cycle, sit e-directed mutagenesis of the consensus C3HC4 zinc finger domain was p erformed, and the effects of these mutations on the growth and replica tion 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 local ization of ICP0, and significantly increases its stability. These muta tions result in severe defects in the growth and DNA replication of re combinant herpesviruses and in their ability to initiate lytic infecti ons at low multiplicities of infection. These viruses, at low multipli cities of infection, synthesize wild-type levels of the IE proteins IC P0 and ICP4 at early times postinfection yet exhibit significant decre ases in the synthesis of the essential IE protein ICP27. These finding s reveal a role for ICP0 in the expression of ICP27 and suggest that t he multiplicity-dependent growth of alpha 0 mutant viruses results par tially from reduced levels of ICP27.