REACTIVATION OF TRANSCRIPTION FROM A VACCINIA VIRUS EARLY PROMOTER LATE IN INFECTION

We have studied the kinetics of RNA synthesis from the vaccinia virus 7,500-molecular-weight gene (7.5K gene) which is regulated by early an d late promoters arranged in tandem. Unexpectedly, after a first burst of RNA synthesis early in infection, transcription was reactivated la te in infection. Reactivation was not dependent on the location of the promoter in the genome or on the presence of the upstream late regula tory sequences. The mRNA synthesized from the reactivated promoter in the late phase had the same 5' and 3' ends as the molecules transcribe d in the early phase. Interestingly, these molecules were efficiently translated despite the absence of the poly(A) leader characteristic of late mRNAs. Reactivation appears to be dependent on virus assembly si nce it is prevented by rifampin, a specific inhibitor of morphogenesis . Finally, analysis of various other early genes showed that reactivat ion is not unique to the 7.5K early promoter.