Members of the Steroid Hormone Receptor Superfamily Interact with TFIIB (S300-II)

The S300-II factor was discovered as an activator of ovalbumin gene transcription with the chicken ovalbumin upstream promoter-transcription factor (COUP-TF, Sagami, I., Tsai, S. Y., Wang, H., Tsai, M.-J., and O'Malley, B. W. (1986) Mol. Cell. Biol. 6, 4259-4267). Although S300-II does not bind DNA selectively, it stabilizes the binding of COUP-TF to its ciselement (Tsai, S. Y., Sagami, I., Wang, H., Tsai, M.-J., and O'Malley, B. W. (1987) Cell 50, 701-709). Purified S300-II is also required for steroid receptor-activated transcription. Cloning and sequencing of S300-II showed that it is the general transcription factor TFIIB. Specific protein-protein interactions between recombinant S300-II/TFIIB and three members of the steroid hormone receptor superfamily, COUP-TF, estrogen receptor, and progesterone receptor, indicate that S300-II/TFIIB is one of the targets of these transactivators. Interestingly, a truncated estrogen receptor construct containing only the N-terminal transcription activation function 1 did not interact with S300-II/TFIIB in our assay, revealing that individual transcription activation functions of a single steroid hormone receptor may contact different targets. Demonstration of a direct association of S300-II/TFIIB and COUP-TF, independent of additional "adaptor" proteins, suggests that members of the steroid hromone receptor superfamily facilitate the transcription of activated genes at least in part via protein-protein interactions with the general transcription factor TFIIB.