ACTIVATION DOMAINS OF TRANSCRIPTION FACTORS MEDIATE REPLICATION DEPENDENT TRANSCRIPTION FROM A MINIMAL HIV-1 PROMOTER

Transcription from a minimal HIV-1 promoter containing the three Sp1 b inding sites and TATA box can be activated without Tat by template DNA replication, Here we show that this activation can also be mediated b y recombinant GAL4 fusion proteins containing the activation domains o f Spl, VP16 or CTF (or by full-length GAL4) targeted to the HIV-I prom oter by replacing the Spl sites with five GAL4 binding sites. Thus Spl is not unique in its ability to mediate replication activated transcr iption, although the degree of processivity elicited by the different activators varied significantly from strongly processive (GAL4-VP16) t o relatively non-processive (GAL4-Sp1 or -CTF), Processive GAL4-VP16-a ctivated transcription, but not efficient initiation, required multipl e GAL4 binding sites, In the presence of Tat, transcription with GAL4- SP1 and GAL4-CTF was further activated (principally at the level of pr ocessivity) but GAL4-VP16-potentiated transcription was only slightly stimulated, The Tat-dependent switch from non-processive to fully proc essive transcription was particularly marked for GAL4-Sp1, an effect w hich may be relevant to the selection of Sp1 binding sites by the HIV- 1 promoter.