Control of abundance of immediate-early mRNA in herpesvirus (pseudorabies)-infected cells

Abstract

In cycloheximide-treated cells, transcription of the pseudorabies virus genome is limited to one small region; a similarly restricted transcript can also be detected at very early stages of the normal infective process (Feldman et al., Virology 97, 316–327, 1979) . In the present report, we show that immediate-early transcripts synthesized in cycloheximide-treated cells and those synthesized in untreated cells during the earliest stages of infection have similar sedimentation characteristics. Thus, the immediate-early transcripts accumulating in cycloheximide-treated cells are probably very similar to those synthesized during the normal course of infection. Pulse-labeling experiments with nuclear monolayers indicate that between 50 and 90 min postinfection the immediate-early region of the genome is not transcribed. However, by 3 hr postinfection, sequences similar to the immediate-early sequences are again transcribed. The transcripts originating from the region specifying for IE RNA that are synthesized at later times after infection are not transported to the cytoplasm; these transcripts also have higher sedimentation characteristics than do the immediate-early transcripts. Immediate-early RNA accumulating in the cells up to 35 min postinfection is stable during a 1-hr chase in actinomycin D. However, by 60 min postinfection, this RNA has become destabilized and turns over, indicating that an early virus function may be responsible for the destabilization of the immediate-early mRNA. As a whole, these results show that the control of abundance of immediate-early RNA occurs at several levels: (1) transcription, (2) processing (movement to the cytoplasm of the transcripts), and (3) stability.