TRANSCRIPTION OF THE GENOME OF PSEUDORABIES VIRUS (A-HERPESVIRUS) IS STRICTLY CONTROLLED

Rabbit kidney [RK] cells infected with pseudorabies virus in the presence of cycloheximide synthesize RNA complementary only to a restricted part of the viral genome. This immediate-early (IE) RNA is complementary to 10% of the viral genome as determined by hybridization in solution. Blot hybridization showed that IE RNA accumulating in the cells during a 5 h labeling period hybridizes only to the ends of the inverted repeat regions of the viral DNA. IE RNA synthesized during a 13 min labeling period in intact cells or a 2 min labeling period in nuclear monolayers also hybridized to these regions of the genome only, indicating that an unstable class of viral RNA is not made and subsequently degraded in cycloheximide-treated, infected cells. Synthesis of IE RNA is detectable by 30 min post-infection during the normal course of infection and continues until about 50 min postinfection. Early RNA is first transcribed at 40 min postinfection and transcription continues thereafter. A switch in the transcriptional program from the synthesis of IE RNA to that of early RNA was also demonstrated following removal of cycloheximide. Late RNA labeled from 6-9 h postinfection or RNA synthesized in nuclear monolayers during a 5 min pulse at 6 h postinfection yields practically identical blot hybridization patterns, indicating that extensive selective degradation of some viral RNA transcripts does not occur at late times after infection. Controls operate at the transcriptional level in Pr virus-infected RK cells.