INTERACTION BETWEEN A TRANSCRIPTIONAL ACTIVATOR AND TRANSCRIPTION FACTOR-IIB INVIVO

TRANSCRIPTION of messenger RNA-encoding genes in vitro requires many protein factors1,2. Transcription factor IID, possibly with the cooperation of TFIIA, binds to the TATA element of the promoter3-5, forming a complex that can bind TFIIB (refs 6, 7) followed by RNA polymerase II (refs 6, 8) and other factors9. One or more of these steps is thought to be facilitated by gene-specific transcriptional activation proteins10-12; this seems to require TFIID-associated auxiliary factors13-15 and may involve direct contact between the activator and TFIID16,17 and/or TFIIB18,19. If such contact is necessary in vivo, activation might conceivably be blocked by a TFIIB derivative containing the sequences necessary for this interaction, but lacking those necessary for binding to the rest of the transcriptional apparatus, an effect similar to that referred to as squelching20 or transcriptional interference21. Here we show that the activity of the glutamine-rich fushi tarazu activation domain is indeed blocked by truncated TFIIB derivatives in Drosophila Schneider L2 cells, suggesting that it is mediated by interactions with TFIIB.