Interaction between a transcriptional activator and transcription factor IIB in vivo.

Transcription of messenger RNA-encoding genes in vitro requires many protein factors. Transcription factor IID, possibly with the cooperation of TFIIA, binds to the TATA element of the promoter, forming a complex that can bind TFIIB (refs 6, 7) followed by RNA polymerase II (refs 6, 8) and other factors. One or more of these steps is thought to be facilitated by gene-specific transcriptional activation proteins; this seems to require TFIID-associated auxiliary factors and may involve direct contact between the activator and TFIID and/or TFIIB. 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 squelching or transcriptional interference. 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.