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J. Biol. Chem., Vol. 275, Issue 52, 40797-40803, December 29, 2000
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From the Departments of Internal Medicine and Biochemistry, Ryburn
Center for Molecular Cardiology, University of Texas Southwestern
Medical Center, Dallas, Texas 75390-8573
The yeast Gal4 protein, like many activators,
binds TATA-binding protein (TBP) directly in vitro. It has
been speculated that this protein-protein interaction is important for
Gal4p-mediated activation of transcription, but little work has been
done to test specific models involving this interaction. In this study, the effect of Gal4p on TBP-TATA binding is addressed. Specifically, it
is asked if the Gal4p-TBP interaction can support cooperative binding
of the two factors to promoters. It is easy to see how such an event
could stimulate transcription, particularly from promoters with a
non-consensus TATA box. In vitro, however, a derivative of
Gal4p (Gal4-(1-93+768-881)) containing the DNA-binding, dimerization, and activation domains does not bind to promoter DNA
cooperatively with either recombinant, purified TBP, or with protein
from a yeast crude extract. In vivo, reporter gene
experiments using promoters with differing TBP affinities reveal no
major Gal4p-mediated stimulation of TBP function from weak TATA boxes, as would be predicted if the proteins bind cooperatively. Furthermore, native Gal4p and a potent Gal4p-based artificial activator lacking a
TBP-binding activation domain support similar ratios of transcription from a series of promoters identical except for mutations in the TATA
box. It is concluded that Gal4p and TBP do not bind cooperatively to
promoters and that this mechanism does not contribute substantially to
Gal4p-mediated transcriptional activation.
To whom correspondence should be addressed: Depts. of Internal
Medicine and Biochemistry, Ryburn Center for Molecular Cardiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8573. Tel.: 214-648-1239; Fax: 214-648-1450; E-mail: thomas.kodadek@utsouthwestern.edu.
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