Differential dependence of herpes simplex virus immediate-early gene expression on de novo-infected cell protein synthesis.

The time course of accumulation of herpes simplex virus immediate-early (IE) mRNA and the requirement for infected cell protein synthesis for mRNA transcription and accumulation were compared. Measurements of transcription in nuclear run-on assays, accumulation of cytoplasmic mRNA by Northern (RNA) blot hybridization, and rates of infected cell protein synthesis by pulse-labeling did not indicate differences among the five IE gene, consistent with previous studies. However, as a result of varying the amount of de novo protein synthesis after infection, at least three patterns of maximal expression of the IE genes were revealed. Addition of the protein synthesis inhibitor anisomycin to cells coincident with infection resulted in maximal rates of transcription and accumulation of functional ICP0 mRNA, while 0.5 h of infected cell protein synthesis prior to addition of the drug was required for maximal expression of ICP22/47 and ICP27 mRNAs. Maximal expression of ICP4 mRNA occurred only when 1 h of de novo protein synthesis occurred prior to the addition of the drug. These results are discussed in the context of alternative mechanisms for regulating IE gene expression.

Accumulation of herpes simplex virus type 1 RNAs of different kinetic classes in the cytoplasm of infected cells.

We have analyzed the accumulation of herpes simplex virus type 1 RNA of the immediate early (IE; infected cell polypeptide types 4 and 0 [ICP-4 and ICP-0]), early (thymidine kinase), and early late (ICP-5) kinetic classes in the cytoplasm of infected cells in the presence of anisomycin, canavanine, or phosphonoacetic acid and in the course of a normal infection. IE RNAs were overproduced and were the only class of transcript detected in anisomycin-blocked cells. Phosphonoacetic acid treatment resulted in overaccumulation of early RNAs and underaccumulation of early late RNAs. Although low-stringency canavanine treatment resulted in accumulation of RNA from all kinetic classes, high-stringency conditions restricted accumulation of herpes simplex virus type 1 RNAs to the IE class. More importantly, the IE RNAs for ICP-4 and ICP-0 accumulated to a lesser extent under high-stringency canavanine conditions compared with their accumulation in anisomycin-treated cells. Therefore, the absence of newly synthesized viral proteins (anisomysin treatment) and the presence of analog proteins (stringent canavanine treatment) have different consequences with regard to the accumulation of these two IE RNAs. The kinetics of cytoplasmic accumulation for these RNAs was different for each class of RNA. The IE RNAs were detectable at 1 h postinfection and reached a maximum accumulation at ca. 3 h postinfection. The IE RNAs for both ICP-4 and ICP-0 persisted at late times of infection; however, they differed in that the RNA for ICP-4 remained at relatively low levels and the RNA for ICP-0 remained at relatively high levels as compared with their peak levels of accumulation. The 1.4-kilobase RNA for the herpes simplex virus type 1 thymidine kinase was detected by 2 h, with maximum accumulation occurring at ca. 5 h postinfection. After the peak of accumulation, the amount of thymidine kinase RNA declined rapidly from 8 to 14 h postinfection. The early late RNA for ICP-5 was detected between 2 and 3 h, after which accumulation increased to a peak between 8 and 10 h postinfection. The level of ICP-5 RNA remained at close to the peak level until 14 h postinfection. We also compared the accumulation of viral mRNAs in the cytoplasm with the rates of synthesis of their respective polypeptides. Our results suggest that translational controls may be involved in the regulation of IE genes but not early or late genes.