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Mol. Cell. Biol., 05 1997, 2538-2549, Vol 17, No. 5
WV Ding and SA Johnston
The transcriptional activation function of the Saccharomyces cerevisiae
activator Gal4p is known to rely on a DNA binding activity at its amino
terminus and an activation domain at its carboxy terminus. Although both
domains are required for activation, truncated forms of Gal4p containing
only these domains activate poorly in vivo. Also, mutations in an internal
conserved region of Gal4p inactivate the protein, suggesting that this
internal region has some function critical to the activity of Gal4p. We
have addressed the question of what is the minimal form of Gal4 protein
that can perform all of its known functions. A form with an internal
deletion of the internal conserved domain of Gal4p is transcriptionally
inactive, allowing selection for suppressors. All suppressors isolated were
intragenic alterations that had further amino acid deletions (miniGAL4s).
Characterization of the most active miniGal4 proteins demonstrated that
they possess all of the known functions of full-length Gal4p, including
glucose repression, galactose induction, response to deletions of gal11 or
gal6, and interactions with other proteins such as Ga180p, Sug1p, and TATA
binding protein. Analysis of the transcriptional activities, protein
levels, and DNA binding abilities of these miniGal4ps and a series of
defined internal mutants compared to those of the full-length Gal4p
indicates that the DNA binding and activation domains are necessary and
sufficient qualitatively for all of these known functions of Gal4p. Our
observations imply that the internal region of Gal4 protein may serve as a
spacer to augment transcription and/or may be involved in intramolecular or
Gal4p-Gal4p interactions.
Copyright © 1997, American Society for Microbiology
The DNA binding and activation domains of Gal4p are sufficient for conveying its regulatory signals
Department of Internal Medicine, University of Texas-Southwestern Medical Center, Dallas 75235-8573, USA.
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