PROPERTIES OF INITIATOR-ASSOCIATED TRANSCRIPTION MEDIATED BY GAL4-VP16

Transcription associated with a terminal deoxynucleotide transferase g ene initiator element is shown to respond to the transcription factor GAL4-VP16 both in vivo and in vitro. High-level transcription requires both an intact initiator element and bound activator. Transcription f rom this initiator-directed promoter is synergistic in vivo in that fi ve GAL4 DNA binding sites yield 36 times the expression of a single si te. Promoters dominated by initiator and TATA elements respond similar ly to several GAL4-based activators, including GAL4-Sp1, GAL4-CTF, GAL 4(1-147), GAL4-p53, GAL4-C/EBP, and GAL4-ER(EF), as well as GAL4-VP16 and Sp1. These and other similarities suggest that primary activation of TATA- and initiator-dominated promoters occurs at common steps. Sin ce the initial assembly steps do not appear to be common for the two p romoter types, the results place interesting constraints on models for how activation occurs.