REPRESSION OF GENE-EXPRESSION UPON INFECTION OF CELLS WITH HERPES-SIMPLEX VIRUS TYPE-1 MUTANTS IMPAIRED FOR IMMEDIATE-EARLY PROTEIN-SYNTHESIS

Herpes simplex virus type 1 (HSV-1) mutants defective in immediate-ear ly (IE) gene expression do not readily enter productive replication af ter infection of tissue culture cells. Instead, their genomes are reta ined in a quiescent, nonreplicating state in which the production of v iral gene products cannot be detected, To investigate the block to vir us replication, we used the HSV-1 triple mutant in 1820K, which, under appropriate conditions, is effectively devoid of the transactivators VP16 (a virion protein), ICP0, and ICP4 (both IE proteins), Promoters for the HSV-1 IE ICP0 gene or the human cytomegalovirus (HCMV) major I E gene, cloned upstream of the Escherichia coli lacZ coding sequences, were introduced into the in 1820K genome. The regulation of these pro moters and of the endogenous HSV-I IE promoters was investigated upon conversion of the virus to a quiescent state. Within 24 h of infection , the ICP0 promoter became much less sensitive to transactivation by V P16 whereas the same element, when used to transform Vero cells, retai ned its responsiveness. The HCMV IE promoter, which is not activated b y VP16, also became less sensitive to the HCMV functional homolog of V P16. Both elements remained available for transactivation by HSV-1 IE proteins at 24 h postinfection, showing that the in 1820K genome was n ot irreversibly inactivated, The promoters controlling the HSV-I ICP I , ICP22, and ICP27 genes also became essentially unresponsive to trans activation by VP16, The ICP0 promoter was induced when hexamethylene b isacetamide was added to cultures at the time of infection, but the re sponse to this agent was also lost by 24 h after infection, Therefore, promoter elements within the HSV-1 genome are actively repressed in t he absence of IE gene expression, and repression is not restricted spe cifically to HSV-1 IE promoters.