Regulation of Herpesvirus Macromolecular Synthesis I. Cascade Regulation of the Synthesis of Three Groups of Viral Proteins

Based on evidence that 50% of herpes simplex 1 DNA is transcribed in HEp-2 cells in the absence of protein synthesis we examined the order and rates of synthesis of viral polypeptides in infected cells after reversal of cycloheximide- or puromycin-mediated inhibition of protein synthesis. These experiments showed that viral polypeptides formed three sequentially synthesized, coordinately regulated groups designated alpha, beta, and gamma. Specifically: (i) The alpha group, containing one minor structural and several nonstructural polypeptides, was synthesized at highest rates from 3 to 4 h postinfection in untreated cells and at diminishing rates thereafter. The beta group, also containing minor structural and nonstructural polypeptides, was synthesized at highest rates from 5 to 7 h and at decreasing rates thereafter. The gamma group containing major structural polypeptides was synthesized at increasing rates until at least 12 h postinfection. (ii) The synthesis of alpha polypeptides did not require prior infected cell protein synthesis. In contrast, the synthesis of beta polypeptides required both prior alpha polypeptide synthesis as well as new RNA synthesis, since the addition of actinomycin D immediately after removal of cycloheximide precluded beta polypeptide synthesis. The function supplied by the alpha polypeptides was stable since interruption of protein synthesis after alpha polypeptide synthesis began and before beta polypeptides were made did not prevent the immediate synthesis of beta polypeptides once the drug was withdrawn. The requirement of gamma polypeptide synthesis for prior synthesis of beta polypeptides seemed to be similar to that of beta polypeptides for prior synthesis of the alpha group. (iii) The rates of synthesis of alpha polypeptides were highest immediately after removal of cycloheximide and declined thereafter concomitant with the initiation of beta polypeptide synthesis; this decline in alpha polypeptide synthesis was less rapid in the presence of actinomycin D which prevented the appearance of beta and gamma polypeptides. The decrease in rates of synthesis of beta polypeptides normally occurring after 7 h postinfection was also less rapid in the presence of actinomycin D than in its absence, whereas ongoing synthesis of gamma polypeptides at this time was rapidly reduced by actinomycin D. (iv) Inhibitors of DNA synthesis (cytosine arabinoside or hydroxyurea) did not prevent the synthesis of alpha, beta, or gamma polypeptides, but did reduce the amounts of gamma polypeptides made.