CIS-ACTING AND TRANS-ACTING ELEMENTS INVOLVED IN REACTIVATION OF VACCINIA VIRUS EARLY TRANSCRIPTION

We have previously shown that transcription from the vaccinia virus 7. 5K early promoter is reactivated late in infection (J. Garces, K. Mast ernak, B. Kunz, and R. Wittek, J. Virol. 67:5394-5401, 1993). To ident ify the sequence elements mediating reactivation, we constructed recom binant viruses harboring deletions, substitutions, or insertions in th e 7.5K promoter or its flanking regions, The analysis of these viruses showed that sequences both upstream as well as downstream of the tran scription initiation site contribute to reactivation of the 7.5K promo ter. We tested whether reactivation could be explained by a high affin ity of vaccinia virus early transcription factor to reactivated promot ers. Bandshift experiments using purified protein showed that promoter s which bind the factor,vith high affinity in general also have high e arly transcriptional activity, However, no correlation was found betwe en affinity of the factor and reactivation. Interestingly, overexpress ion of recombinant early transcription factor in vaccinia virus-infect ed cells resulted in a shutdown of late transcription and in reactivat ion of promoters, which are normally not reactivated.